Module sqlselect 

A real SQL SELECT engine — expressions, aliases, CASE, functions, joins.

Why this module exists

The pgwire layer translates SQL text into NQL text. That works beautifully for SELECT col FROM t WHERE x = 1, and it cannot be stretched any further: NQL has no expressions, no table aliases, no CASE, no scalar functions and no joins. Those are not missing features of the translation — they are things the target language cannot say.

And they are exactly what catalogue introspection is made of. psql’s \dt is one statement containing a two-table LEFT JOIN, a nine-branch CASE, two scalar function calls, four qualified column references, an IN list, a !~ regex and ORDER BY 1,2. Every one of those has to work or the command does not.

So this is a small but genuine SQL evaluator: lexer, parser, expression evaluator, nested-loop join. It operates over rows supplied by a callback, which is what lets the same engine serve synthesised catalogue relations today and stored collections later.

What it is NOT

It is not a query planner and does not pretend to be. The join is a nested loop, which is honest for catalogue relations (tens of rows) and would be wrong to point at a large collection without an index strategy. That boundary is enforced by the caller, not hidden here.

The rule this module follows

Anything it cannot evaluate is REFUSED with an error naming the construct. It never guesses. A catalogue query that silently returns the wrong rows produces an empty or wrong table list, and a wrong table list is indistinguishable from a correct one until somebody’s data appears to be missing.

Structs

Bound

One row of a (possibly joined) result: an ordered list of (binding, row-or-NULL).

Join

Opts

Execution options. Every switch exists so a differential test can run the SAME query with the optimisation on and off and compare — without that, a test believing it exercised an optimisation could be measuring the unoptimised path, and the equivalence suite would prove nothing.

OrderBy

OutCol

One output column: the key it is stored under, and the name the client sees.

Select

SelectItem

TableRef

VecRelation

A relation backed by an already-materialised Vec.

Enums

Dir

Expr

JoinKind

Tok

Traits

Relation

A relation, delivered one row at a time.

Functions

eval

Evaluate an expression against one bound row.

execute

Run a parsed SELECT, returning (column names, rows).

execute_explain

Run a parsed SELECT, also reporting how each join was executed.

execute_opts

The full form.

execute_with

As execute_explain, with predicate pushdown switchable.

from_vec

Wrap a materialised relation.

lex

parse

Parse one SELECT statement.

run

Parse and run in one call.

Type Aliases

Resolver

Everything one execution needs from the outside world.