Module subquery 

Subquery Executor

Provides support for nested queries within SQL expressions.

Subquery Types

• Scalar: Single-value subquery x = (SELECT max(y) FROM ...)
• EXISTS: Existence check EXISTS (SELECT * FROM ... WHERE ...)
• IN: Set membership x IN (SELECT y FROM ...)
• NOT IN: Set non-membership
• ANY/ALL: Comparison with set x > ANY (SELECT ...)

Correlation

• Correlated: References outer query columns, evaluated per row
• Non-correlated: Independent, can be evaluated once and cached

Optimization

• Non-correlated subqueries use once-only evaluation
• IN subqueries build hash index for O(1) lookups
• EXISTS short-circuits on first match

Structs

SubqueryDef

A subquery definition

SubqueryExecutor

Subquery executor handles evaluation of nested queries

ValueHash

Hashable wrapper for Value (for HashSet storage)

Enums

CompareOp

Comparison operator for ANY/ALL

SubqueryCache

Cached result of a non-correlated subquery

SubqueryType

Type of subquery

Functions

bind_outer_refs

Check if a binding satisfies correlation constraints

detect_correlation

Detect outer variable references in a subquery