Module subquery 

E5.1 — Correlated subquery decorrelation: EXISTS/IN/scalar subquery analysis.

DataFusion 53 already handles subquery decorrelation for batch queries via the DecorrelatePredicateSubquery optimizer rule. This module adds:

1. AST-level detection of EXISTS/IN/NOT IN/scalar subquery patterns.
2. Streaming guard: rejects correlated subqueries that reference a registered streaming table — DataFusion does not handle these.
3. Kind classification so callers can adapt error messages and explain output.

Structs

DetectedSubquery

A subquery occurrence found in a SQL statement.

Enums

SubqueryKind

Classification of a subquery occurrence detected in a SQL statement.

Functions

detect_subqueries

Analyse sql and return every subquery occurrence.

explain_subqueries

Return a human-readable summary of subquery kinds found in sql.

validate_no_streaming_subqueries

Validate that sql contains no subqueries that reference a streaming table.