Failing test.

core/src/lib.rs

@@ -342,6 +342,12 @@ impl ValueTypeSet {
     }
 }
 
+impl ValueTypeSet {
+    pub fn is_only_numeric(&self) -> bool {
+        self.is_subset(&ValueTypeSet::of_numeric_types())
+    }
+}
+
 impl IntoIterator for ValueTypeSet {
     type Item = ValueType;
     type IntoIter = ::enum_set::Iter<ValueType>;
@@ -367,10 +373,16 @@ impl ::std::iter::Extend<ValueType> for ValueTypeSet {
     }
 }
 
+/// We have an enum of types, `ValueType`. It can be collected into a set, `ValueTypeSet`. Each type
+/// is associated with a type tag, which is how a type is represented in, e.g., SQL storage. Types
+/// can share type tags, because backing SQL storage is able to differentiate between some types
+/// (e.g., longs and doubles), and so distinct tags aren't necessary. That association is defined by
+/// `SQLValueType`. That trait similarly extends to `ValueTypeSet`, which maps a collection of types
+/// into a collection of tags.
 pub trait SQLValueTypeSet {
     fn value_type_tags(&self) -> BTreeSet<ValueTypeTag>;
-    fn has_unique_type_code(&self) -> bool;
-    fn unique_type_code(&self) -> Option<ValueTypeTag>;
+    fn has_unique_type_tag(&self) -> bool;
+    fn unique_type_tag(&self) -> Option<ValueTypeTag>;
 }
 
 impl SQLValueTypeSet for ValueTypeSet {
@@ -383,15 +395,15 @@ impl SQLValueTypeSet for ValueTypeSet {
         out
     }
 
-    fn unique_type_code(&self) -> Option<ValueTypeTag> {
-        if self.is_unit() || self.has_unique_type_code() {
+    fn unique_type_tag(&self) -> Option<ValueTypeTag> {
+        if self.is_unit() || self.has_unique_type_tag() {
             self.exemplar().map(|t| t.value_type_tag())
         } else {
             None
         }
     }
 
-    fn has_unique_type_code(&self) -> bool {
+    fn has_unique_type_tag(&self) -> bool {
         if self.is_unit() {
             return true;
         }

query-algebrizer/src/clauses/mod.rs

@@ -264,6 +264,18 @@ impl Default for ConjoiningClauses {
     }
 }
 
+pub struct VariableIterator<'a>(
+    ::std::collections::btree_map::Keys<'a, Variable, TypedValue>,
+);
+
+impl<'a> Iterator for VariableIterator<'a> {
+    type Item = &'a Variable;
+
+    fn next(&mut self) -> Option<&'a Variable> {
+        self.0.next()
+    }
+}
+
 impl ConjoiningClauses {
     /// Construct a new `ConjoiningClauses` with the provided alias counter. This allows a caller
     /// to share a counter with an enclosing scope, and to start counting at a particular offset
@@ -370,13 +382,13 @@ impl ConjoiningClauses {
     }
 
     /// Return an interator over the variables externally bound to values.
-    pub fn value_bound_variables(&self) -> ::std::collections::btree_map::Keys<Variable, TypedValue> {
-        self.value_bindings.keys()
+    pub fn value_bound_variables(&self) -> VariableIterator {
+        VariableIterator(self.value_bindings.keys())
     }
 
     /// Return a set of the variables externally bound to values.
     pub fn value_bound_variable_set(&self) -> BTreeSet<Variable> {
-        self.value_bindings.keys().cloned().collect()
+        self.value_bound_variables().cloned().collect()
     }
 
     /// Return a single `ValueType` if the given variable is known to have a precise type.

query-algebrizer/src/clauses/predicate.rs

@@ -127,7 +127,7 @@ impl ConjoiningClauses {
         if shared_types == ValueTypeSet::of_one(ValueType::Instant) {
             left_v = self.resolve_instant_argument(&predicate.operator, 0, left)?;
             right_v = self.resolve_instant_argument(&predicate.operator, 1, right)?;
-        } else if !shared_types.is_empty() && shared_types.is_subset(&ValueTypeSet::of_numeric_types()) {
+        } else if !shared_types.is_empty() && shared_types.is_only_numeric() {
             left_v = self.resolve_numeric_argument(&predicate.operator, 0, left)?;
             right_v = self.resolve_numeric_argument(&predicate.operator, 1, right)?;
         } else {

query-algebrizer/src/lib.rs

@@ -62,8 +62,19 @@ pub use types::{
 pub struct AlgebraicQuery {
     default_source: SrcVar,
     pub find_spec: FindSpec,
-    has_aggregates: bool,
+
+    /// The set of variables that the caller wishes to be used for grouping when aggregating.
+    /// These are specified in the query input, as `:with`, and are then chewed up during projection.
+    /// If no variables are supplied, then no additional grouping is necessary beyond the
+    /// non-aggregated projection list.
     pub with: BTreeSet<Variable>,
+
+    /// Some query features, such as ordering, are implemented by implicit reference to SQL columns.
+    /// In order for these references to be 'live', those columns must be projected.
+    /// This is the set of variables that must be so projected.
+    /// This is not necessarily every variable that will be so required -- some variables
+    /// will already be in the projection list.
+    pub named_projection: BTreeSet<Variable>,
     pub order: Option<Vec<OrderBy>>,
     pub limit: Limit,
     pub cc: clauses::ConjoiningClauses,
@@ -187,15 +198,14 @@ pub fn algebrize_with_inputs(schema: &Schema,
     cc.prune_extracted_types();
 
     let (order, extra_vars) = validate_and_simplify_order(&cc, parsed.order)?;
-    let with: BTreeSet<Variable> = parsed.with.into_iter().chain(extra_vars.into_iter()).collect();
 
     // This might leave us with an unused `:in` variable.
     let limit = if parsed.find_spec.is_unit_limited() { Limit::Fixed(1) } else { parsed.limit };
     let q = AlgebraicQuery {
         default_source: parsed.default_source,
         find_spec: parsed.find_spec,
-        has_aggregates: false,           // TODO: we don't parse them yet.
-        with: with,
+        with: parsed.with,
+        named_projection: extra_vars,
         order: order,
         limit: limit,
         cc: cc,

query-parser/src/parse.rs

@@ -38,6 +38,7 @@ use self::mentat_parser_utils::value_and_span::{
 };
 
 use self::mentat_query::{
+    Aggregate,
     Binding,
     Direction,
     Element,
@@ -270,6 +271,13 @@ def_parser!(Query, func, (QueryFunction, Vec<FnArg>), {
     (Query::query_function(), Query::arguments())
 });
 
+def_parser!(Query, aggregate, Aggregate, {
+    seq().of_exactly(Query::func())
+         .map(|(func, args)| Aggregate {
+             func, args,
+         })
+});
+
 /// A vector containing just a parenthesized filter expression.
 def_parser!(Where, pred, WhereClause, {
     // Accept either a nested list or a nested vector here:
@@ -376,6 +384,7 @@ def_matches_plain_symbol!(Find, placeholder, "_");
 
 def_parser!(Find, elem, Element, {
     Query::variable().map(Element::Variable)
+                     .or(Query::aggregate().map(Element::Aggregate))
 });
 
 def_parser!(Find, find_scalar, FindSpec, {

query-projector/src/lib.rs

@@ -19,7 +19,9 @@ extern crate mentat_query_algebrizer;
 extern crate mentat_query_sql;
 extern crate mentat_sql;
 
+use std::collections::BTreeSet;
 use std::iter;
+
 use rusqlite::{
     Row,
     Rows,
@@ -39,9 +41,12 @@ use mentat_db::{
 };
 
 use mentat_query::{
+    Aggregate,
     Element,
     FindSpec,
     Limit,
+    PlainSymbol,
+    QueryFunction,
     Variable,
 };
 
@@ -49,11 +54,14 @@ use mentat_query_algebrizer::{
     AlgebraicQuery,
     ColumnName,
     ConjoiningClauses,
+    QualifiedAlias,
     VariableColumn,
 };
 
 use mentat_query_sql::{
     ColumnOrExpression,
+    Expression,
+    GroupBy,
     Name,
     Projection,
     ProjectedColumn,
@@ -64,6 +72,31 @@ error_chain! {
         Error, ErrorKind, ResultExt, Result;
     }
 
+    errors {
+        /// We're just not done yet.  Message that the feature is recognized but not yet
+        /// implemented.
+        NotYetImplemented(t: String) {
+            description("not yet implemented")
+            display("not yet implemented: {}", t)
+        }
+        CannotProjectImpossibleBinding(op: SimpleAggregationOp) {
+            description("no possible types for variable in projection list")
+            display("no possible types for value provided to {:?}", op)
+        }
+        CannotApplyAggregateOperationToTypes(op: SimpleAggregationOp, types: ValueTypeSet) {
+            description("cannot apply projection operation to types")
+            display("cannot apply projection operation {:?} to types {:?}", op, types)
+        }
+        UnboundVariable(var: PlainSymbol) {
+            description("cannot project unbound variable")
+            display("cannot project unbound variable {:?}", var)
+        }
+        NoTypeAvailableForVariable(var: PlainSymbol) {
+            description("cannot find type for variable")
+            display("cannot find type for variable {:?}", var)
+        }
+    }
+
     foreign_links {
         Rusqlite(rusqlite::Error);
     }
@@ -133,16 +166,16 @@ impl TypedIndex {
     /// Look up this index and type(index) pair in the provided row.
     /// This function will panic if:
     ///
-    /// - This is an `Unknown` and the retrieved type code isn't an i32.
+    /// - This is an `Unknown` and the retrieved type tag isn't an i32.
     /// - If the retrieved value can't be coerced to a rusqlite `Value`.
     /// - Either index is out of bounds.
     ///
-    /// Because we construct our SQL projection list, the code that stored the data, and this
+    /// Because we construct our SQL projection list, the tag that stored the data, and this
     /// consumer, a panic here implies that we have a bad bug — we put data of a very wrong type in
     /// a row, and thus can't coerce to Value, we're retrieving from the wrong place, or our
     /// generated SQL is junk.
     ///
-    /// This function will return a runtime error if the type code is unknown, or the value is
+    /// This function will return a runtime error if the type tag is unknown, or the value is
     /// otherwise not convertible by the DB layer.
     fn lookup<'a, 'stmt>(&self, row: &Row<'a, 'stmt>) -> Result<TypedValue> {
         use TypedIndex::*;
@@ -161,17 +194,22 @@ impl TypedIndex {
     }
 }
 
-fn candidate_column(cc: &ConjoiningClauses, var: &Variable) -> (ColumnOrExpression, Name) {
+fn cc_column(cc: &ConjoiningClauses, var: &Variable) -> Result<QualifiedAlias> {
+    cc.column_bindings
+      .get(var)
+      .and_then(|cols| cols.get(0).cloned())
+      .ok_or_else(|| ErrorKind::UnboundVariable(var.name()).into())
+}
+
+fn candidate_column(cc: &ConjoiningClauses, var: &Variable) -> Result<(ColumnOrExpression, Name)> {
     // Every variable should be bound by the top-level CC to at least
     // one column in the query. If that constraint is violated it's a
     // bug in our code, so it's appropriate to panic here.
-    let columns = cc.column_bindings
-                    .get(var)
-                    .expect(format!("Every variable should have a binding, but {:?} does not", var).as_str());
-
-    let qa = columns[0].clone();
-    let name = VariableColumn::Variable(var.clone()).column_name();
-    (ColumnOrExpression::Column(qa), name)
+    cc_column(cc, var)
+        .map(|qa| {
+            let name = VariableColumn::Variable(var.clone()).column_name();
+            (ColumnOrExpression::Column(qa), name)
+        })
 }
 
 fn candidate_type_column(cc: &ConjoiningClauses, var: &Variable) -> (ColumnOrExpression, Name) {
@@ -183,21 +221,207 @@ fn candidate_type_column(cc: &ConjoiningClauses, var: &Variable) -> (ColumnOrExp
 }
 
 /// Return the projected column -- that is, a value or SQL column and an associated name -- for a
-/// given variable. Also return the type, if known.
+/// given variable. Also return the type.
 /// Callers are expected to determine whether to project a type tag as an additional SQL column.
-pub fn projected_column_for_var(var: &Variable, cc: &ConjoiningClauses) -> (ProjectedColumn, Option<ValueType>) {
+pub fn projected_column_for_var(var: &Variable, cc: &ConjoiningClauses) -> Result<(ProjectedColumn, ValueTypeSet)> {
     if let Some(value) = cc.bound_value(&var) {
         // If we already know the value, then our lives are easy.
         let tag = value.value_type();
         let name = VariableColumn::Variable(var.clone()).column_name();
-        (ProjectedColumn(ColumnOrExpression::Value(value.clone()), name), Some(tag))
+        Ok((ProjectedColumn(ColumnOrExpression::Value(value.clone()), name), ValueTypeSet::of_one(tag)))
     } else {
         // If we don't, then the CC *must* have bound the variable.
-        let (column, name) = candidate_column(cc, var);
-        (ProjectedColumn(column, name), cc.known_type(var))
+        let (column, name) = candidate_column(cc, var)?;
+        Ok((ProjectedColumn(column, name), cc.known_type_set(var)))
     }
 }
 
+fn projected_column_for_simple_aggregate(simple: &SimpleAggregate, cc: &ConjoiningClauses) -> Result<(ProjectedColumn, ValueType)> {
+    let known_types = cc.known_type_set(&simple.var);
+    let return_type = simple.op.is_applicable_to_types(known_types)?;
+    let projected_column_or_expression =
+        if let Some(value) = cc.bound_value(&simple.var) {
+            // Oh, we already know the value!
+            if simple.use_static_value() {
+                // We can statically compute the aggregate result for some operators -- not count or
+                // sum, but avg/max/min are OK.
+                ColumnOrExpression::Value(value)
+            } else {
+                let expression = Expression::Unary {
+                    sql_op: simple.op.to_sql(),
+                    arg: ColumnOrExpression::Value(value),
+                };
+                ColumnOrExpression::Expression(Box::new(expression), return_type)
+            }
+        } else {
+            // The common case: the values are bound during execution.
+            let column = cc_column(cc, &simple.var)?;
+            let expression = Expression::Unary {
+                sql_op: simple.op.to_sql(),
+                arg: ColumnOrExpression::Column(column),
+            };
+            ColumnOrExpression::Expression(Box::new(expression), return_type)
+        };
+    Ok((ProjectedColumn(projected_column_or_expression, simple.column_name()), return_type))
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum SimpleAggregationOp {
+    Avg,
+    Count,
+    Max,
+    Min,
+    Sum,
+}
+
+impl SimpleAggregationOp {
+    fn to_sql(&self) -> &'static str {
+        use SimpleAggregationOp::*;
+        match self {
+            &Avg => "avg",
+            &Count => "count",
+            &Max => "max",
+            &Min => "min",
+            &Sum => "sum",
+        }
+    }
+
+    fn for_function(function: &QueryFunction) -> Option<SimpleAggregationOp> {
+        match function.0.plain_name() {
+            "avg" => Some(SimpleAggregationOp::Avg),
+            "count" => Some(SimpleAggregationOp::Count),
+            "max" => Some(SimpleAggregationOp::Max),
+            "min" => Some(SimpleAggregationOp::Min),
+            "sum" => Some(SimpleAggregationOp::Sum),
+            _ => None,
+        }
+    }
+
+    /// With knowledge of the types to which a variable might be bound,
+    /// return a `Result` to determine whether this aggregation is suitable.
+    /// For example, it's valid to take the `Avg` of `{Double, Long}`, invalid
+    /// to take `Sum` of `{Instant}`, valid to take (lexicographic) `Max` of `{String}`,
+    /// but invalid to take `Max` of `{Uuid, String}`.
+    ///
+    /// The returned type is the type of the result of the aggregation.
+    fn is_applicable_to_types(&self, possibilities: ValueTypeSet) -> Result<ValueType> {
+        use SimpleAggregationOp::*;
+        if possibilities.is_empty() {
+            bail!(ErrorKind::CannotProjectImpossibleBinding(*self))
+        }
+
+        match self {
+            // One can always count results.
+            &Count => Ok(ValueType::Long),
+
+            // Only numeric types can be averaged or summed.
+            &Avg => {
+                if possibilities.is_only_numeric() {
+                    // The mean of a set of numeric values will always, for our purposes, be a double.
+                    Ok(ValueType::Double)
+                } else {
+                    bail!(ErrorKind::CannotApplyAggregateOperationToTypes(*self, possibilities))
+                }
+            },
+            &Sum => {
+                if possibilities.is_only_numeric() {
+                    if possibilities.contains(ValueType::Double) {
+                        Ok(ValueType::Double)
+                    } else {
+                        // TODO: BigInt.
+                        Ok(ValueType::Long)
+                    }
+                } else {
+                    bail!(ErrorKind::CannotApplyAggregateOperationToTypes(*self, possibilities))
+                }
+            },
+
+            &Max | &Min => {
+                if possibilities.is_unit() {
+                    use ValueType::*;
+                    let the_type = possibilities.exemplar().expect("a type");
+                    match the_type {
+                        // These types are numerically ordered.
+                        Double | Long | Instant => Ok(the_type),
+
+                        // Boolean: false < true.
+                        Boolean => Ok(the_type),
+
+                        // String: lexicographic order.
+                        String => Ok(the_type),
+
+                        // These types are unordered.
+                        Keyword | Ref | Uuid => {
+                            bail!(ErrorKind::CannotApplyAggregateOperationToTypes(*self, possibilities))
+                        },
+                    }
+                } else {
+                    // It cannot be empty -- we checked.
+                    // The only types that are valid to compare cross-type are numbers.
+                    if possibilities.is_only_numeric() {
+                        // Note that if the max/min is a Long, it will be returned as a Double!
+                        if possibilities.contains(ValueType::Double) {
+                            Ok(ValueType::Double)
+                        } else {
+                            // TODO: BigInt.
+                            Ok(ValueType::Long)
+                        }
+                    } else {
+                        bail!(ErrorKind::CannotApplyAggregateOperationToTypes(*self, possibilities))
+                    }
+                }
+            },
+        }
+    }
+}
+
+struct SimpleAggregate {
+    op: SimpleAggregationOp,
+    var: Variable,
+}
+
+impl SimpleAggregate {
+    fn column_name(&self) -> Name {
+        format!("({} {})", self.op.to_sql(), self.var.name())
+    }
+
+    fn use_static_value(&self) -> bool {
+        use SimpleAggregationOp::*;
+        match self.op {
+            Avg | Max | Min => true,
+            Count | Sum => false,
+        }
+    }
+}
+
+trait SimpleAggregation {
+    fn to_simple(&self) -> Option<SimpleAggregate>;
+}
+
+impl SimpleAggregation for Aggregate {
+    fn to_simple(&self) -> Option<SimpleAggregate> {
+        if self.args.len() != 1 {
+            return None;
+        }
+        self.args[0]
+            .as_variable()
+            .and_then(|v| SimpleAggregationOp::for_function(&self.func)
+                              .map(|op| SimpleAggregate { op, var: v.clone(), }))
+    }
+}
+
+/// An internal temporary struct to pass between the projection 'walk' and the
+/// resultant projector.
+/// Projection accumulates three things:
+/// - A SQL projection list.
+/// - A collection of templates for the projector to use to extract values.
+/// - A list of columns to use for grouping. Grouping is a property of the projection!
+struct ProjectedElements {
+    sql_projection: Projection,
+    templates: Vec<TypedIndex>,
+    group_by: Vec<GroupBy>,
+}
+
 /// Walk an iterator of `Element`s, collecting projector templates and columns.
 ///
 /// Returns a pair: the SQL projection (which should always be a `Projection::Columns`)
@@ -213,26 +437,44 @@ pub fn projected_column_for_var(var: &Variable, cc: &ConjoiningClauses) -> (Proj
 fn project_elements<'a, I: IntoIterator<Item = &'a Element>>(
     count: usize,
     elements: I,
-    query: &AlgebraicQuery) -> Result<(Projection, Vec<TypedIndex>)> {
+    query: &AlgebraicQuery) -> Result<ProjectedElements> {
 
     let mut cols = Vec::with_capacity(count);
     let mut i: i32 = 0;
     let mut templates = vec![];
-    let mut with = query.with.clone();
 
+    // "Query variables not in aggregate expressions will group the results and appear intact
+    // in the result."
+    // Compute the set of variables projected by the query, then subtract
+    // those used in aggregate expressions. This will be our GROUP BY clause.
+    // The GROUP BY clause should begin with any non-projected :with variables, in order,
+    // then the non-aggregated projected variables, in order.
+
+    // Predetermined:
+    // extras: variables needed for ORDER BY. query.named_projection.
+    // with: variables to be used for grouping. query.with.
+    //
+    // Accumulated:
+    // variables: variables in the projection list.
+    // aggregated: variables used in aggregates.
+
+    // Results:
+    // group_by: (with + variables) - aggregated
+    // extra_projection: (with + extras) - variables
+
+    let mut aggregated = BTreeSet::new();
+    let mut variables = BTreeSet::new();
     for e in elements {
         match e {
             // Each time we come across a variable, we push a SQL column
             // into the SQL projection, aliased to the name of the variable,
             // and we push an annotated index into the projector.
             &Element::Variable(ref var) => {
-                // If we're projecting this, we don't need it in :with.
-                with.remove(var);
+                variables.insert(var.clone());
 
-                let (projected_column, maybe_type) = projected_column_for_var(&var, &query.cc);
+                let (projected_column, type_set) = projected_column_for_var(&var, &query.cc)?;
                 cols.push(projected_column);
-                if let Some(ty) = maybe_type {
-                    let tag = ty.value_type_tag();
+                if let Some(tag) = type_set.unique_type_tag() {
                     templates.push(TypedIndex::Known(i, tag));
                     i += 1;     // We used one SQL column.
                 } else {
@@ -243,23 +485,114 @@ fn project_elements<'a, I: IntoIterator<Item = &'a Element>>(
                     let (type_column, type_name) = candidate_type_column(&query.cc, &var);
                     cols.push(ProjectedColumn(type_column, type_name));
                 }
-            }
+            },
+            &Element::Aggregate(ref a) => {
+                if let Some(simple) = a.to_simple() {
+                    aggregated.insert(simple.var.clone());
+
+                    // When we encounter a simple aggregate -- one in which the aggregation can be
+                    // implemented in SQL, on a single variable -- we just push the SQL aggregation op.
+                    // We must ensure the following:
+                    // - There's a column for the var.
+                    // - The type of the var is known to be restricted to a sensible input set
+                    //   (not necessarily a single type, but e.g., all vals must be Double or Long).
+                    // - The type set must be appropriate for the operation. E.g., `Sum` is not a
+                    //   meaningful operation on instants.
+
+                    let (projected_column, return_type) = projected_column_for_simple_aggregate(&simple, &query.cc)?;
+                    cols.push(projected_column);
+
+                    // We might regret using the type tag here instead of the `ValueType`.
+                    templates.push(TypedIndex::Known(i, return_type.value_type_tag()));
+                    i += 1;
+                } else {
+                    // TODO: complex aggregates.
+                    bail!(ErrorKind::NotYetImplemented("complex aggregates".into()));
+                }
+            },
         }
     }
 
-    for var in with {
-        // We need to collect these into the SQL column list, but they don't affect projection.
-        // If a variable is of a non-fixed type, also project the type tag column, so we don't
-        // accidentally unify across types when considering uniqueness!
-        let (column, name) = candidate_column(&query.cc, &var);
+    // Anything we're projecting, or that's part of an aggregate, doesn't need to be in GROUP BY.
+    //
+    // Anything used in ORDER BY (which we're given in `named_projection`)
+    // needs to be in the SQL column list so we can refer to it by name.
+    //
+    // They don't affect projection.
+    //
+    // If a variable is of a non-fixed type, also project the type tag column, so we don't
+    // accidentally unify across types when considering uniqueness!
+    // Similarly, the type tag needs to be grouped.
+    // extra_projection: extras - variables
+    for var in query.named_projection.iter() {
+        if variables.contains(var) {
+            continue;
+        }
+
+        // If it's a fixed value, we need do nothing further.
+        if query.cc.is_value_bound(&var) {
+            continue;
+        }
+
+        let (column, name) = candidate_column(&query.cc, &var)?;
         cols.push(ProjectedColumn(column, name));
-        if query.cc.known_type(&var).is_none() {
+
+        // We don't care if a column has a single _type_, we care if it has a single type _tag_,
+        // because that's what we'll use if we're projecting. E.g., Long and Double.
+        // Single type implies single type tag, and is cheaper, so we check that first.
+        let types = query.cc.known_type_set(&var);
+        if !types.has_unique_type_tag() {
             let (type_column, type_name) = candidate_type_column(&query.cc, &var);
             cols.push(ProjectedColumn(type_column, type_name));
         }
     }
 
-    Ok((Projection::Columns(cols), templates))
+    if aggregated.is_empty() {
+        // We're done -- we never need to group unless we're aggregating.
+        return Ok(ProjectedElements {
+                      sql_projection: Projection::Columns(cols),
+                      templates,
+                      group_by: vec![],
+                  });
+    }
+
+    // group_by: (with + variables) - aggregated
+    let mut group_by_vars: BTreeSet<Variable> = query.with.union(&variables).cloned().collect();
+    for var in aggregated.iter() {
+        group_by_vars.remove(var);
+    }
+
+    // We never need to group by a constant.
+    for var in query.cc.value_bound_variables() {
+        group_by_vars.remove(&var);
+    }
+
+    // Turn this collection of vars into a collection of columns from the query.
+    // We don't allow grouping on anything but a variable bound in the query.
+    // We group by tag if necessary.
+    let mut group_by = Vec::with_capacity(2 * group_by_vars.len());
+
+    for var in group_by_vars {
+        let types = query.cc.known_type_set(&var);
+        if !types.has_unique_type_tag() {
+            // Group by type then SQL value.
+            let type_col = query.cc
+                                .extracted_types
+                                .get(&var)
+                                .cloned()
+                                .map(GroupBy::QueryColumn)
+                                .ok_or_else(|| ErrorKind::NoTypeAvailableForVariable(var.name().clone()))?;
+            group_by.push(type_col);
+        }
+        let val_col = cc_column(&query.cc, &var).map(GroupBy::QueryColumn)?;
+        group_by.push(val_col);
+    }
+
+    Ok(ProjectedElements {
+        sql_projection: Projection::Columns(cols),
+        templates,
+        group_by,
+    })
 }
 
 pub trait Projector {
@@ -295,12 +628,13 @@ impl ScalarProjector {
         }
     }
 
-    fn combine(sql: Projection, mut templates: Vec<TypedIndex>) -> Result<CombinedProjection> {
-        let template = templates.pop().expect("Expected a single template");
+    fn combine(mut elements: ProjectedElements) -> Result<CombinedProjection> {
+        let template = elements.templates.pop().expect("Expected a single template");
         Ok(CombinedProjection {
-            sql_projection: sql,
+            sql_projection: elements.sql_projection,
             datalog_projector: Box::new(ScalarProjector::with_template(template)),
             distinct: false,
+            group_by_cols: elements.group_by,
         })
     }
 }
@@ -333,19 +667,22 @@ impl TupleProjector {
 
     // This is exactly the same as for rel.
     fn collect_bindings<'a, 'stmt>(&self, row: Row<'a, 'stmt>) -> Result<Vec<TypedValue>> {
-        assert_eq!(row.column_count(), self.len as i32);
+        // gte 'cos we might be querying extra columns for ordering.
+        // The templates will take care of ignoring columns.
+        assert!(row.column_count() >= self.len as i32);
         self.templates
             .iter()
             .map(|ti| ti.lookup(&row))
             .collect::<Result<Vec<TypedValue>>>()
     }
 
-    fn combine(column_count: usize, sql: Projection, templates: Vec<TypedIndex>) -> Result<CombinedProjection> {
-        let p = TupleProjector::with_templates(column_count, templates);
+    fn combine(column_count: usize, elements: ProjectedElements) -> Result<CombinedProjection> {
+        let p = TupleProjector::with_templates(column_count, elements.templates);
         Ok(CombinedProjection {
-            sql_projection: sql,
+            sql_projection: elements.sql_projection,
             datalog_projector: Box::new(p),
             distinct: false,
+            group_by_cols: elements.group_by,
         })
     }
 }
@@ -381,19 +718,22 @@ impl RelProjector {
     }
 
     fn collect_bindings<'a, 'stmt>(&self, row: Row<'a, 'stmt>) -> Result<Vec<TypedValue>> {
-        assert_eq!(row.column_count(), self.len as i32);
+        // gte 'cos we might be querying extra columns for ordering.
+        // The templates will take care of ignoring columns.
+        assert!(row.column_count() >= self.len as i32);
         self.templates
             .iter()
             .map(|ti| ti.lookup(&row))
             .collect::<Result<Vec<TypedValue>>>()
     }
 
-    fn combine(column_count: usize, sql: Projection, templates: Vec<TypedIndex>) -> Result<CombinedProjection> {
-        let p = RelProjector::with_templates(column_count, templates);
+    fn combine(column_count: usize, elements: ProjectedElements) -> Result<CombinedProjection> {
+        let p = RelProjector::with_templates(column_count, elements.templates);
         Ok(CombinedProjection {
-            sql_projection: sql,
+            sql_projection: elements.sql_projection,
             datalog_projector: Box::new(p),
             distinct: true,
+            group_by_cols: elements.group_by,
         })
     }
 }
@@ -423,12 +763,13 @@ impl CollProjector {
         }
     }
 
-    fn combine(sql: Projection, mut templates: Vec<TypedIndex>) -> Result<CombinedProjection> {
-        let template = templates.pop().expect("Expected a single template");
+    fn combine(mut elements: ProjectedElements) -> Result<CombinedProjection> {
+        let template = elements.templates.pop().expect("Expected a single template");
         Ok(CombinedProjection {
-            sql_projection: sql,
+            sql_projection: elements.sql_projection,
             datalog_projector: Box::new(CollProjector::with_template(template)),
             distinct: true,
+            group_by_cols: elements.group_by,
         })
     }
 }
@@ -458,6 +799,9 @@ pub struct CombinedProjection {
 
     /// True if this query requires the SQL query to include DISTINCT.
     pub distinct: bool,
+
+    // A list of column names to use as a GROUP BY clause.
+    pub group_by_cols: Vec<GroupBy>,
 }
 
 impl CombinedProjection {
@@ -488,29 +832,30 @@ pub fn query_projection(query: &AlgebraicQuery) -> Result<CombinedProjection> {
             sql_projection: Projection::One,
             datalog_projector: Box::new(constant_projector),
             distinct: false,
+            group_by_cols: vec![],
         })
     } else {
         match query.find_spec {
             FindColl(ref element) => {
-                let (cols, templates) = project_elements(1, iter::once(element), query)?;
-                CollProjector::combine(cols, templates).map(|p| p.flip_distinct_for_limit(&query.limit))
+                let e = project_elements(1, iter::once(element), query)?;
+                CollProjector::combine(e).map(|p| p.flip_distinct_for_limit(&query.limit))
             },
 
             FindScalar(ref element) => {
-                let (cols, templates) = project_elements(1, iter::once(element), query)?;
-                ScalarProjector::combine(cols, templates)
+                let e = project_elements(1, iter::once(element), query)?;
+                ScalarProjector::combine(e)
             },
 
             FindRel(ref elements) => {
                 let column_count = query.find_spec.expected_column_count();
-                let (cols, templates) = project_elements(column_count, elements, query)?;
-                RelProjector::combine(column_count, cols, templates).map(|p| p.flip_distinct_for_limit(&query.limit))
+                let e = project_elements(column_count, elements, query)?;
+                RelProjector::combine(column_count, e).map(|p| p.flip_distinct_for_limit(&query.limit))
             },
 
             FindTuple(ref elements) => {
                 let column_count = query.find_spec.expected_column_count();
-                let (cols, templates) = project_elements(column_count, elements, query)?;
-                TupleProjector::combine(column_count, cols, templates)
+                let e = project_elements(column_count, elements, query)?;
+                TupleProjector::combine(column_count, e)
             },
         }
     }

query-projector/tests/aggregates.rs

@@ -0,0 +1,87 @@
+// Copyright 2016 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+extern crate mentat_core;
+extern crate mentat_query;
+extern crate mentat_query_algebrizer;
+extern crate mentat_query_parser;
+extern crate mentat_query_projector;
+
+use mentat_core::{
+    Attribute,
+    Entid,
+    Schema,
+    ValueType,
+};
+
+use mentat_query_parser::{
+    parse_find_string,
+};
+
+use mentat_query::{
+    NamespacedKeyword,
+};
+
+use mentat_query_algebrizer::{
+    algebrize,
+};
+
+use mentat_query_projector::{
+    query_projection,
+};
+
+// These are helpers that tests use to build Schema instances.
+fn associate_ident(schema: &mut Schema, i: NamespacedKeyword, e: Entid) {
+    schema.entid_map.insert(e, i.clone());
+    schema.ident_map.insert(i.clone(), e);
+}
+
+fn add_attribute(schema: &mut Schema, e: Entid, a: Attribute) {
+    schema.schema_map.insert(e, a);
+}
+
+fn prepopulated_schema() -> Schema {
+    let mut schema = Schema::default();
+    associate_ident(&mut schema, NamespacedKeyword::new("foo", "name"), 65);
+    associate_ident(&mut schema, NamespacedKeyword::new("foo", "age"), 68);
+    associate_ident(&mut schema, NamespacedKeyword::new("foo", "height"), 69);
+    add_attribute(&mut schema, 65, Attribute {
+        value_type: ValueType::String,
+        multival: false,
+        ..Default::default()
+    });
+    add_attribute(&mut schema, 68, Attribute {
+        value_type: ValueType::Long,
+        multival: false,
+        ..Default::default()
+    });
+    add_attribute(&mut schema, 69, Attribute {
+        value_type: ValueType::Long,
+        multival: false,
+        ..Default::default()
+    });
+    schema
+}
+
+#[test]
+fn test_aggregate_unsuitable_type() {
+    let schema = prepopulated_schema();
+
+    let query = r#"[:find (avg ?e)
+                    :where
+                    [?e :foo/age ?a]]"#;
+
+    // While the query itself algebrizes and parses…
+    let parsed = parse_find_string(query).expect("query input to have parsed");
+    let algebrized = algebrize(&schema, parsed).expect("query algebrizes");
+
+    // … when we look at the projection list, we cannot reconcile the types.
+    assert!(query_projection(&algebrized).is_err());
+}

query-sql/src/lib.rs

@@ -15,10 +15,10 @@ extern crate mentat_query_algebrizer;
 extern crate mentat_sql;
 
 use std::boxed::Box;
-
 use mentat_core::{
     Entid,
     TypedValue,
+    ValueType,
 };
 
 use mentat_query::{
@@ -60,6 +60,11 @@ pub enum ColumnOrExpression {
     Integer(i32),       // We use these for type codes etc.
     Long(i64),
     Value(TypedValue),
+    Expression(Box<Expression>, ValueType),      // Track the return type.
+}
+
+pub enum Expression {
+    Unary { sql_op: &'static str, arg: ColumnOrExpression },
 }
 
 /// `QueryValue` and `ColumnOrExpression` are almost identical… merge somehow?
@@ -84,6 +89,26 @@ pub enum Projection {
     One,
 }
 
+#[derive(PartialEq, Eq)]
+pub enum GroupBy {
+    ProjectedColumn(Name),
+    QueryColumn(QualifiedAlias),
+    // TODO: non-projected expressions, etc.
+}
+
+impl QueryFragment for GroupBy {
+    fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
+        match self {
+            &GroupBy::ProjectedColumn(ref name) => {
+                out.push_identifier(name.as_str())
+            },
+            &GroupBy::QueryColumn(ref qa) => {
+                qualified_alias_push_sql(out, qa)
+            },
+        }
+    }
+}
+
 #[derive(Copy, Clone)]
 pub struct Op(pub &'static str);      // TODO: we can do better than this!
 
@@ -185,6 +210,7 @@ pub struct SelectQuery {
     pub projection: Projection,
     pub from: FromClause,
     pub constraints: Vec<Constraint>,
+    pub group_by: Vec<GroupBy>,
     pub order: Vec<OrderBy>,
     pub limit: Limit,
 }
@@ -257,10 +283,8 @@ impl QueryFragment for ColumnOrExpression {
     fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
         use self::ColumnOrExpression::*;
         match self {
-            &Column(QualifiedAlias(ref table, ref column)) => {
-                out.push_identifier(table.as_str())?;
-                out.push_sql(".");
-                push_column(out, column)
+            &Column(ref qa) => {
+                qualified_alias_push_sql(out, qa)
             },
             &Entid(entid) => {
                 out.push_sql(entid.to_string().as_str());
@@ -277,6 +301,23 @@ impl QueryFragment for ColumnOrExpression {
             &Value(ref v) => {
                 out.push_typed_value(v)
             },
+            &Expression(ref e, _) => {
+                e.push_sql(out)
+            },
+        }
+    }
+}
+
+impl QueryFragment for Expression {
+    fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
+        match self {
+            &Expression::Unary { ref sql_op, ref arg } => {
+                out.push_sql(sql_op);              // No need to escape built-ins.
+                out.push_sql("(");
+                arg.push_sql(out)?;
+                out.push_sql(")");
+                Ok(())
+            },
         }
     }
 }
@@ -379,6 +420,13 @@ impl QueryFragment for JoinOp {
     }
 }
 
+// We don't own QualifiedAlias or QueryFragment, so we can't implement the trait.
+fn qualified_alias_push_sql(out: &mut QueryBuilder, qa: &QualifiedAlias) -> BuildQueryResult {
+    out.push_identifier(qa.0.as_str())?;
+    out.push_sql(".");
+    push_column(out, &qa.1)
+}
+
 // We don't own SourceAlias or QueryFragment, so we can't implement the trait.
 fn source_alias_push_sql(out: &mut QueryBuilder, sa: &SourceAlias) -> BuildQueryResult {
     let &SourceAlias(ref table, ref alias) = sa;
@@ -527,6 +575,16 @@ impl QueryFragment for SelectQuery {
                        { out.push_sql(" AND ") });
         }
 
+        match &self.group_by {
+            group_by if !group_by.is_empty() => {
+                out.push_sql(" GROUP BY ");
+                interpose!(group, group_by,
+                           { group.push_sql(out)? },
+                           { out.push_sql(", ") });
+            },
+            _ => {},
+        }
+
         if !self.order.is_empty() {
             out.push_sql(" ORDER BY ");
             interpose!(&OrderBy(ref dir, ref var), self.order,
@@ -727,6 +785,7 @@ mod tests {
                     right: ColumnOrExpression::Entid(65536),
                 },
             ],
+            group_by: vec![],
             order: vec![],
             limit: Limit::None,
         };

query-translator/src/translate.rs

@@ -15,7 +15,9 @@ use mentat_core::{
     ValueType,
 };
 
-use mentat_query::Limit;
+use mentat_query::{
+    Limit,
+};
 
 use mentat_query_algebrizer::{
     AlgebraicQuery,
@@ -47,6 +49,7 @@ use mentat_query_sql::{
     ColumnOrExpression,
     Constraint,
     FromClause,
+    GroupBy,
     Op,
     ProjectedColumn,
     Projection,
@@ -214,7 +217,8 @@ fn table_for_computed(computed: ComputedTable, alias: TableAlias) -> TableOrSubq
                         // project it as the variable name.
                         // E.g., SELECT datoms03.v AS `?x`.
                         for var in projection.iter() {
-                            let (projected_column, maybe_type) = projected_column_for_var(var, &cc);
+                            // TODO: chain results out.
+                            let (projected_column, type_set) = projected_column_for_var(var, &cc).expect("every var to be bound");
                             columns.push(projected_column);
 
                             // Similarly, project type tags if they're not known conclusively in the
@@ -222,10 +226,10 @@ fn table_for_computed(computed: ComputedTable, alias: TableAlias) -> TableOrSubq
                             // Assumption: we'll never need to project a tag without projecting the value of a variable.
                             if type_extraction.contains(var) {
                                 let expression =
-                                    if let Some(ty) = maybe_type {
+                                    if let Some(tag) = type_set.unique_type_tag() {
                                         // If we know the type for sure, just project the constant.
                                         // SELECT datoms03.v AS `?x`, 10 AS `?x_value_type_tag`
-                                        ColumnOrExpression::Integer(ty.value_type_tag())
+                                        ColumnOrExpression::Integer(tag)
                                     } else {
                                         // Otherwise, we'll have an established type binding! This'll be
                                         // either a datoms table or, recursively, a subquery. Project
@@ -246,7 +250,7 @@ fn table_for_computed(computed: ComputedTable, alias: TableAlias) -> TableOrSubq
                         // Each arm simply turns into a subquery.
                         // The SQL translation will stuff "UNION" between each arm.
                         let projection = Projection::Columns(columns);
-                        cc_to_select_query(projection, cc, false, None, Limit::None)
+                        cc_to_select_query(projection, cc, false, vec![], None, Limit::None)
                   }).collect(),
                 alias)
         },
@@ -268,6 +272,7 @@ fn table_for_computed(computed: ComputedTable, alias: TableAlias) -> TableOrSubq
 fn cc_to_select_query(projection: Projection,
                       cc: ConjoiningClauses,
                       distinct: bool,
+                      group_by: Vec<GroupBy>,
                       order: Option<Vec<OrderBy>>,
                       limit: Limit) -> SelectQuery {
     let from = if cc.from.is_empty() {
@@ -303,6 +308,7 @@ fn cc_to_select_query(projection: Projection,
         distinct: distinct,
         projection: projection,
         from: from,
+        group_by: group_by,
         constraints: cc.wheres
                        .into_iter()
                        .map(|c| c.to_constraint())
@@ -321,12 +327,13 @@ pub fn cc_to_exists(cc: ConjoiningClauses) -> SelectQuery {
             distinct: false,
             projection: Projection::One,
             from: FromClause::Nothing,
+            group_by: vec![],
             constraints: vec![],
             order: vec![],
             limit: Limit::None,
         }
     } else {
-        cc_to_select_query(Projection::One, cc, false, None, Limit::None)
+        cc_to_select_query(Projection::One, cc, false, vec![], None, Limit::None)
     }
 }
 
@@ -335,9 +342,9 @@ pub fn cc_to_exists(cc: ConjoiningClauses) -> SelectQuery {
 pub fn query_to_select(query: AlgebraicQuery) -> Result<ProjectedSelect> {
     // TODO: we can't pass `query.limit` here if we aggregate during projection.
     // SQL-based aggregation -- `SELECT SUM(datoms00.e)` -- is fine.
-    let CombinedProjection { sql_projection, datalog_projector, distinct } = query_projection(&query)?;
+    let CombinedProjection { sql_projection, datalog_projector, distinct, group_by_cols } = query_projection(&query)?;
     Ok(ProjectedSelect {
-        query: cc_to_select_query(sql_projection, query.cc, distinct, query.order, query.limit),
+        query: cc_to_select_query(sql_projection, query.cc, distinct, group_by_cols, query.order, query.limit),
         projector: datalog_projector,
     })
 }

query-translator/tests/translate.rs

@@ -191,7 +191,7 @@ fn test_bound_variable_limit_affects_types() {
     assert_eq!(Some(ValueType::Long),
                algebrized.cc.known_type(&Variable::from_valid_name("?limit")));
 
-    let select = query_to_select(algebrized).expect("query to translate");
+    let select = query_to_select(algebrized).expect("query to successfully translate");
     let SQLQuery { sql, args } = select.query.to_sql_query().unwrap();
 
     // TODO: this query isn't actually correct -- we don't yet algebrize for variables that are
@@ -546,13 +546,13 @@ fn test_with_without_aggregate() {
     // Known type.
     let query = r#"[:find ?x :with ?y :where [?x :foo/bar ?y]]"#;
     let SQLQuery { sql, args } = translate(&schema, query);
-    assert_eq!(sql, "SELECT DISTINCT `datoms00`.e AS `?x`, `datoms00`.v AS `?y` FROM `datoms` AS `datoms00` WHERE `datoms00`.a = 99");
+    assert_eq!(sql, "SELECT DISTINCT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.a = 99");
     assert_eq!(args, vec![]);
 
     // Unknown type.
     let query = r#"[:find ?x :with ?y :where [?x _ ?y]]"#;
     let SQLQuery { sql, args } = translate(&schema, query);
-    assert_eq!(sql, "SELECT DISTINCT `all_datoms00`.e AS `?x`, `all_datoms00`.v AS `?y`, `all_datoms00`.value_type_tag AS `?y_value_type_tag` FROM `all_datoms` AS `all_datoms00`");
+    assert_eq!(sql, "SELECT DISTINCT `all_datoms00`.e AS `?x` FROM `all_datoms` AS `all_datoms00`");
     assert_eq!(args, vec![]);
 }
 
@@ -754,6 +754,55 @@ fn test_unbound_attribute_with_ground() {
                                                       `all_datoms00`.value_type_tag = 5)");
 }
 
+/*
+#[test]
+fn test_colliding_values_unbound_types() {
+    let schema = prepopulated_schema();
+    let query = r#"[:find ?x ?a ?y
+                    :where
+                    [?x _ ?y]
+                    [?a _ ?y]]"#;
+    let SQLQuery { sql, .. } = translate(&schema, query);
+    assert_eq!(sql, "SELECT DISTINCT `all_datoms00`.e AS `?x`, \
+                                     `all_datoms01`.e AS `?a`, \
+                                     `all_datoms00`.v AS `?y`, \
+                                     `all_datoms00`.value_type_tag AS `?y_value_type_tag` \
+                     FROM `all_datoms` AS `all_datoms00`, `all_datoms` AS `all_datoms01` \
+                     WHERE `all_datoms00`.v = `all_datoms01`.v \
+                       AND `all_datoms00`.value_type_tag = `all_datoms01`.value_type_tag");
+}
+
+#[test]
+fn test_restricted_types() {
+    let schema = prepopulated_schema();
+    let query = r#"[:find ?x ?y
+                    :where
+                    [?x _ ?y]
+                    [(< ?y 10)]]"#;
+    let SQLQuery { sql, .. } = translate(&schema, query);
+
+    // #385: use `datoms` instead of `all_datoms`.
+    // No need to project the type code -- long and double are distinguishable.
+    assert_eq!(sql, "SELECT DISTINCT `all_datoms00`.e AS `?x`, \
+                                     `all_datoms00`.v AS `?y` \
+                     FROM `all_datoms` AS `all_datoms00` \
+                     WHERE `all_datoms00`.v < 10 \
+                       AND `all_datoms00`.value_type_tag = 5");
+}
+
+#[test]
+fn test_known_type_range() {
+    let schema = prepopulated_schema();
+    let query = r#"[:find ?x ?y :where [?x :foo/bar] [?y _ ?x]]"#;
+    let SQLQuery { sql, .. } = translate(&schema, query);
+    assert_eq!(sql, "SELECT DISTINCT `datoms00`.e AS `?x`, \
+                                     `datoms00`.e AS `?y` \
+                     FROM `datoms` AS `datoms00`, `datoms` AS `datoms01` \
+                     WHERE `datoms00`.a = 66 \
+                       AND `datoms01`.v = `datoms00`.e \
+                       AND `datoms01`.value_type_tag = 1");
+}
+*/
 
 #[test]
 fn test_not_with_ground() {
@@ -955,3 +1004,30 @@ fn test_instant_range() {
                        AND `datoms00`.v > 1497574601257000");
     assert_eq!(args, vec![]);
 }
+
+#[test]
+fn test_project_aggregates() {
+    let schema = prepopulated_typed_schema(ValueType::Long);
+    let query = r#"[:find ?e (max ?t)
+                    :where
+                    [?e :foo/bar ?t]]"#;
+    let SQLQuery { sql, args } = translate(&schema, query);
+    assert_eq!(sql, "SELECT DISTINCT `datoms00`.e AS `?e`, max(`datoms00`.v) AS `(max ?t)` \
+                     FROM \
+                     `datoms` AS `datoms00` \
+                     WHERE `datoms00`.a = 99 \
+                     GROUP BY `datoms00`.e");
+    assert_eq!(args, vec![]);
+
+    let query = r#"[:find (max ?t)
+                    :with ?e
+                    :where
+                    [?e :foo/bar ?t]]"#;
+    let SQLQuery { sql, args } = translate(&schema, query);
+    assert_eq!(sql, "SELECT DISTINCT max(`datoms00`.v) AS `(max ?t)` \
+                     FROM \
+                     `datoms` AS `datoms00` \
+                     WHERE `datoms00`.a = 99 \
+                     GROUP BY `datoms00`.e");
+    assert_eq!(args, vec![]);
+}

query/src/lib.rs

@@ -428,17 +428,16 @@ pub struct Pull {
 }
 */
 
-/*
+#[derive(Debug, Eq, PartialEq)]
 pub struct Aggregate {
-    pub fn_name: String,
+    pub func: QueryFunction,
     pub args: Vec<FnArg>,
 }
-*/
 
 #[derive(Debug, Eq, PartialEq)]
 pub enum Element {
     Variable(Variable),
-    // Aggregate(Aggregate),   // TODO
+    Aggregate(Aggregate),
     // Pull(Pull),             // TODO
 }
 

src/query.rs

@@ -84,6 +84,7 @@ pub fn q_once<'sqlite, 'schema, 'query, T>
     let select = query_to_select(algebrized)?;
     let SQLQuery { sql, args } = select.query.to_sql_query()?;
 
+println!("SQL: {:?}", sql);
     let mut statement = sqlite.prepare(sql.as_str())?;
 
     let rows = if args.is_empty() {

tests/query.rs

@@ -361,7 +361,8 @@ fn test_fulltext() {
                  _ => panic!("Unexpected results."),
             }
         },
-        _ => panic!("Expected query to work."),
+        Result::Ok(r) => panic!("Unexpected results {:?}.", r),
+        Result::Err(e) => panic!("Expected query to work, got {:?}.", e),
     }
 
     let a = conn.transact(&mut c, r#"[[:db/add "a" :foo/term "talk"]]"#)
@@ -454,3 +455,303 @@ fn test_instant_range_query() {
         _ => panic!("Expected query to work."),
     }
 }
+
+#[test]
+fn test_aggregation_implicit_grouping() {
+    let mut c = new_connection("").expect("Couldn't open conn.");
+    let mut conn = Conn::connect(&mut c).expect("Couldn't open DB.");
+
+    conn.transact(&mut c, r#"[
+        [:db/add "a" :db/ident :foo/score]
+        [:db/add "a" :db/valueType :db.type/long]
+        [:db/add "a" :db/cardinality :db.cardinality/one]
+        [:db/add "b" :db/ident :foo/name]
+        [:db/add "b" :db/valueType :db.type/string]
+        [:db/add "b" :db/cardinality :db.cardinality/one]
+        [:db/add "c" :db/ident :foo/is-vegetarian]
+        [:db/add "c" :db/valueType :db.type/boolean]
+        [:db/add "c" :db/cardinality :db.cardinality/one]
+        [:db/add "d" :db/ident :foo/play]
+        [:db/add "d" :db/valueType :db.type/ref]
+        [:db/add "d" :db/cardinality :db.cardinality/many]
+        [:db/add "d" :db/unique :db.unique/value]
+    ]"#).unwrap();
+
+    let ids = conn.transact(&mut c, r#"[
+        [:db/add "a" :foo/name "Alice"]
+        [:db/add "b" :foo/name "Beli"]
+        [:db/add "c" :foo/name "Carlos"]
+        [:db/add "d" :foo/name "Diana"]
+        [:db/add "a" :foo/is-vegetarian true]
+        [:db/add "b" :foo/is-vegetarian true]
+        [:db/add "c" :foo/is-vegetarian false]
+        [:db/add "d" :foo/is-vegetarian false]
+        [:db/add "aa" :foo/score 14]
+        [:db/add "ab" :foo/score 99]
+        [:db/add "ac" :foo/score 14]
+        [:db/add "ba" :foo/score 22]
+        [:db/add "bb" :foo/score 11]
+        [:db/add "ca" :foo/score 42]
+        [:db/add "da" :foo/score 5]
+        [:db/add "db" :foo/score 28]
+        [:db/add "d"  :foo/play "da"]
+        [:db/add "d"  :foo/play "db"]
+        [:db/add "a"  :foo/play "aa"]
+        [:db/add "a"  :foo/play "ab"]
+        [:db/add "a"  :foo/play "ac"]
+        [:db/add "b"  :foo/play "ba"]
+        [:db/add "b"  :foo/play "bb"]
+        [:db/add "c"  :foo/play "ca"]
+    ]"#).unwrap().tempids;
+
+    // We can combine these aggregates.
+    let r = conn.q_once(&mut c,
+                        r#"[:find ?x ?name (max ?score) (count ?score) (avg ?score)
+                            :where
+                            [?x :foo/name ?name]
+                            [?x :foo/play ?game]
+                            [?game :foo/score ?score]
+                            ]"#, None);
+    match r {
+        Result::Ok(QueryResults::Rel(vals)) => {
+            assert_eq!(vals,
+                vec![
+                    vec![TypedValue::Ref(ids.get("a").cloned().unwrap()),
+                         TypedValue::String("Alice".to_string().into()),
+                         TypedValue::Long(99),
+                         TypedValue::Long(3),
+                         TypedValue::Double((127f64 / 3f64).into())],
+                    vec![TypedValue::Ref(ids.get("b").cloned().unwrap()),
+                         TypedValue::String("Beli".to_string().into()),
+                         TypedValue::Long(22),
+                         TypedValue::Long(2),
+                         TypedValue::Double((33f64 / 2f64).into())],
+                    vec![TypedValue::Ref(ids.get("c").cloned().unwrap()),
+                         TypedValue::String("Carlos".to_string().into()),
+                         TypedValue::Long(42),
+                         TypedValue::Long(1),
+                         TypedValue::Double(42f64.into())],
+                    vec![TypedValue::Ref(ids.get("d").cloned().unwrap()),
+                         TypedValue::String("Diana".to_string().into()),
+                         TypedValue::Long(28),
+                         TypedValue::Long(2),
+                         TypedValue::Double((33f64 / 2f64).into())]]);
+        },
+        Result::Ok(x) => panic!("Got unexpected results {:?}", x),
+        Result::Err(e) => panic!("Expected query to work: got {:?}", e),
+    }
+}
+
+// TODO: this can't be phrased in Datalog!
+/*
+#[test]
+fn test_corresponding_row_value_aggregation() {
+
+    // Who's youngest, via min?
+    let r = conn.q_once(&mut c,
+                        r#"[:find [?name (min ?age)]
+                            :where
+                            [?x :foo/age ?age]
+                            [?x :foo/name ?name]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Tuple(Some(vals))) => {
+            assert_eq!(vals,
+                       vec![TypedValue::String("Alice".to_string().into()),
+                            TypedValue::Long(14)]);
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // Who's oldest, via max?
+    let r = conn.q_once(&mut c,
+                        r#"[:find [?name (max ?age)]
+                            :where
+                            [?x :foo/age ?age]
+                            [?x :foo/name ?name]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Tuple(Some(vals))) => {
+            assert_eq!(vals,
+                       vec![TypedValue::String("Carlos".to_string().into()),
+                            TypedValue::Long(42)]);
+        },
+        _ => panic!("Expected query to work."),
+    }
+}
+*/
+
+#[test]
+fn test_simple_aggregation() {
+    let mut c = new_connection("").expect("Couldn't open conn.");
+    let mut conn = Conn::connect(&mut c).expect("Couldn't open DB.");
+
+    conn.transact(&mut c, r#"[
+        [:db/add "a" :db/ident :foo/age]
+        [:db/add "a" :db/valueType :db.type/long]
+        [:db/add "a" :db/cardinality :db.cardinality/one]
+        [:db/add "b" :db/ident :foo/name]
+        [:db/add "b" :db/valueType :db.type/string]
+        [:db/add "b" :db/cardinality :db.cardinality/one]
+        [:db/add "c" :db/ident :foo/is-vegetarian]
+        [:db/add "c" :db/valueType :db.type/boolean]
+        [:db/add "c" :db/cardinality :db.cardinality/one]
+    ]"#).unwrap();
+
+    let ids = conn.transact(&mut c, r#"[
+        [:db/add "a" :foo/name "Alice"]
+        [:db/add "b" :foo/name "Beli"]
+        [:db/add "c" :foo/name "Carlos"]
+        [:db/add "d" :foo/name "Diana"]
+        [:db/add "a" :foo/is-vegetarian true]
+        [:db/add "b" :foo/is-vegetarian true]
+        [:db/add "c" :foo/is-vegetarian false]
+        [:db/add "d" :foo/is-vegetarian false]
+        [:db/add "a" :foo/age 14]
+        [:db/add "b" :foo/age 22]
+        [:db/add "c" :foo/age 42]
+        [:db/add "d" :foo/age 28]
+    ]"#).unwrap().tempids;
+
+    // Count how many vegetarians there are. This is not the same as `count-distinct`.
+    // Note the distinction between including `:with` and not.
+    let r = conn.q_once(&mut c,
+                        r#"[:find (count ?veg)
+                            :where
+                            [_ :foo/is-vegetarian ?veg]
+                            [(ground true) ?veg]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Rel(vals)) => {
+            assert_eq!(vals, vec![vec![TypedValue::Long(1)]]);
+        },
+        Result::Ok(r) => panic!("Expected query to work, got {:?}", r),
+        Result::Err(e) => panic!("Expected query to work, got {:?}", e),
+    }
+
+    let r = conn.q_once(&mut c,
+                        r#"[:find (count ?veg) .
+                            :with ?person
+                            :where
+                            [?person :foo/is-vegetarian ?veg]
+                            [(ground true) ?veg]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Scalar(Some(val))) => {
+            assert_eq!(val, TypedValue::Long(2));
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // What are the oldest and youngest ages?
+    let r = conn.q_once(&mut c,
+                        r#"[:find [(min ?age) (max ?age)]
+                            :where
+                            [_ :foo/age ?age]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Tuple(Some(vals))) => {
+            assert_eq!(vals,
+                       vec![TypedValue::Long(14),
+                            TypedValue::Long(42)]);
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // Who's youngest, via order?
+    let r = conn.q_once(&mut c,
+                        r#"[:find [?name ?age]
+                            :order (asc ?age)
+                            :where
+                            [?x :foo/age ?age]
+                            [?x :foo/name ?name]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Tuple(Some(vals))) => {
+            assert_eq!(vals,
+                       vec![TypedValue::String("Alice".to_string().into()),
+                            TypedValue::Long(14)]);
+        },
+        Result::Ok(r) => panic!("Unexpected results {:?}", r),
+        Result::Err(e) => panic!("Expected query to work, got {:?}", e),
+    }
+
+    // Who's oldest, via order?
+    let r = conn.q_once(&mut c,
+                        r#"[:find [?name ?age]
+                            :order (desc ?age)
+                            :where
+                            [?x :foo/age ?age]
+                            [?x :foo/name ?name]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Tuple(Some(vals))) => {
+            assert_eq!(vals,
+                       vec![TypedValue::String("Carlos".to_string().into()),
+                            TypedValue::Long(42)]);
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // What's the average age?
+    let r = conn.q_once(&mut c,
+                        r#"[:find (avg ?age) .
+                            :where
+                            [_ :foo/age ?age]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Scalar(Some(sum))) => {
+            assert_eq!(sum, TypedValue::Double(26.5f64.into()));
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // What's the total age?
+    let r = conn.q_once(&mut c,
+                        r#"[:find (sum ?age) .
+                            :where
+                            [_ :foo/age ?age]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Scalar(Some(sum))) => {
+            assert_eq!(sum, TypedValue::Long(106));
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // How many distinct names are there?
+    let r = conn.q_once(&mut c,
+                        r#"[:find (count ?name) .
+                            :where
+                            [_ :foo/name ?name]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Scalar(Some(count))) => {
+            assert_eq!(count, TypedValue::Long(4));
+        },
+        _ => panic!("Expected query to work."),
+    }
+
+    // We can use constraints, too.
+    // What's the average age of adults?
+    let r = conn.q_once(&mut c,
+                        r#"[:find [(avg ?age) (count ?age)]
+                            :where
+                            [_ :foo/age ?age]
+                            [(>= ?age 18)]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Tuple(Some(vals))) => {
+            assert_eq!(vals, vec![TypedValue::Double((92f64 / 3f64).into()),
+                                  TypedValue::Long(3)]);
+        },
+        Result::Ok(x) => panic!("Got unexpected results {:?}", x),
+        Result::Err(e) => panic!("Expected query to work: got {:?}", e),
+    }
+
+    // Who's oldest, vegetarians or not?
+    let r = conn.q_once(&mut c,
+                        r#"[:find ?veg (max ?age)
+                            :where
+                            [?p :foo/age ?age]
+                            [?p :foo/is-vegetarian ?veg]]"#, None);
+    match r {
+        Result::Ok(QueryResults::Rel(vals)) => {
+            assert_eq!(vals, vec![
+                vec![TypedValue::Boolean(false), TypedValue::Long(42)],
+                vec![TypedValue::Boolean(true), TypedValue::Long(22)],
+            ]);
+        },
+        Result::Ok(x) => panic!("Got unexpected results {:?}", x),
+        Result::Err(e) => panic!("Expected query to work: got {:?}", e),
+    }
+}