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merge_subqueries

polyglot_sql::optimizer::subquery

Function merge_subqueries 

Source 
pub fn merge_subqueries(
    expression: Expression,
    leave_tables_isolated: bool,
) -> Expression
Expand description

Merge derived tables into outer queries.

This optimization merges subqueries that appear in the FROM clause into the outer query, reducing query complexity.

§Example

-- Before:
SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y
-- After:
SELECT x.a FROM x CROSS JOIN y

§Arguments

  • expression - The expression to optimize
  • leave_tables_isolated - If true, don’t merge if it would result in multiple table selects

§Returns

The optimized expression with merged subqueries