08d2c613a4
This commit: - Defines a new kind of column, distinct from the eavt columns in `DatomsColumn`, to model the rows projected from subqueries. These always name one of two things: a variable, or a variable's type tag. Naturally the two cases are thus `Variable` and `VariableTypeTag`. These are cheap to clone, given that `Variable` is an `Rc<String>`. - Defines `Column` as a wrapper around `DatomsColumn` and `VariableColumn`. Everywhere we used to use `DatomsColumn` we now allow `Column`: particularly in constraints and projections. - Broadens the definition of a table list in the intermediate "query-sql" representation to include a SQL UNION. A UNION is represented as a list of queries and an alias. - Implements translation from a `ComputedTable` to the query-sql representation. In this commit we only project vars, not type tags. Review comment: discuss bind_column_to_var for ValueTypeTag. Review comment: implement From<Vec<T>> for ConsumableVec<T>. |
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This module handles the derivation from an algebrized query of two things:
- A SQL projection: a mapping from columns mentioned in the body of the query to columns in the output.
- A Datalog projection: a function that consumes rows of the appropriate shape (as defined by the SQL projection) to yield one of the four kinds of Datalog query result.
These two must naturally coordinate, and so they are both produced here.