Function try_plan_exists_subquery

nodedb-sql/src/planner/subquery.rs:251–285

Plan `EXISTS (SELECT 1 FROM tbl WHERE tbl.col = outer.col)` as a semi/anti join. Extracts the correlated column from the subquery's WHERE clause.

(
    subquery: &ast::Query,
    negated: bool,
    catalog: &dyn SqlCatalog,
    functions: &FunctionRegistry,
    temporal: crate::TemporalScope,
)

///
/// Extracts the correlated column from the subquery's WHERE clause.
fn try_plan_exists_subquery(
    subquery: &ast::Query,
    negated: bool,
    catalog: &dyn SqlCatalog,
    functions: &FunctionRegistry,
    temporal: crate::TemporalScope,
) -> Result<Option<SubqueryJoin>> {
    let select = match &*subquery.body {
        SetExpr::Select(s) => s,
        _ => return Ok(None),
    };

    // Look for a correlated predicate in the WHERE: inner.col = outer.col
    let (outer_col, inner_col) = match &select.selection {
        Some(expr) => match extract_correlated_eq(expr) {
            Some(pair) => pair,
            None => return Ok(None),
        },
        None => return Ok(None),
    };

    // Build a simplified subquery without the correlated predicate for planning.
    let inner_plan = super::select::plan_query(subquery, catalog, functions, temporal)?;

    Ok(Some(SubqueryJoin {
        outer_column: outer_col,
        inner_plan,
        inner_column: inner_col,
        join_type: if negated {
            JoinType::Anti
        } else {
            JoinType::Semi
        },
    }))
}

/// Extract a correlated equality predicate from a WHERE clause.
///