35d73d5541
This adds an `:order` keyword to `:find`. If present, the results of the query will be an ordered set, rather than an unordered set; rows will appear in an ordered defined by each `:order` entry. Each can be one of three things: - A var, `?x`, meaning "order by ?x ascending". - A pair, `(asc ?x)`, meaning "order by ?x ascending". - A pair, `(desc ?x)`, meaning "order by ?x descending". Values will be ordered in this sequence for asc, and in reverse for desc: 1. Entity IDs, in ascending numerical order. 2. Booleans, false then true. 3. Timestamps, in ascending numerical order. 4. Longs and doubles, intermixed, in ascending numerical order. 5. Strings, in ascending lexicographic order. 6. Keywords, in ascending lexicographic order, considering the entire ns/name pair as a single string separated by '/'. Subcommits: Pre: make bound_value public. Pre: generalize ErrorKind::UnboundVariable for use in order. Part 1: parse (direction, var) pairs. Part 2: parse :order clause into FindQuery. Part 3: include order variables in algebrized query. We add order variables to :with, so we can reuse its type tag projection logic, and so that we can phrase ordering in terms of variables rather than datoms columns. Part 4: produce SQL for order clauses. |
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This crate turns a parsed query, as defined by the query crate and produced by the query-parser crate, into an algebrized tree, also called a query processor tree.
This is something of a wooly definition: a query algebrizer in a traditional relational database is the component that combines the schema — including column type constraints — with the query, resolving names and that sort of thing. Much of that work is unnecessary in our model; for example, we don't need to resolve column aliases, deal with table names, or that sort of thing. But the similarity is strong enough to give us the name of this crate.
The result of this process is traditionally handed to the query optimizer to yield an execution plan. In our case the execution plan is deterministically derived from the algebrized tree, and the real optimization (such as it is) takes place within the underlying SQLite database.