Function extract_correlated_eq

nodedb-sql/src/planner/subquery.rs:292–319

Extract a correlated equality predicate from a WHERE clause. Looks for patterns like `o.user_id = u.id` and returns (outer_col, inner_col). The "inner" column is the one qualified with the subquery's table alias; the "outer" column is the one referencing the outer query's table.

(expr: &Expr)

/// The "inner" column is the one qualified with the subquery's table alias;
/// the "outer" column is the one referencing the outer query's table.
fn extract_correlated_eq(expr: &Expr) -> Option<(String, String)> {
    match expr {
        Expr::BinaryOp {
            left,
            op: ast::BinaryOperator::Eq,
            right,
        } => {
            let left_parts = extract_qualified_column(left);
            let right_parts = extract_qualified_column(right);
            match (left_parts, right_parts) {
                (Some((_lt, lc)), Some((_rt, rc))) => {
                    // Convention: left is inner (subquery table), right is outer.
                    // But we can't distinguish without schema, so just return both.
                    Some((rc, lc))
                }
                _ => None,
            }
        }
        // For AND, try to find a correlated eq in either side.
        Expr::BinaryOp {
            left,
            op: ast::BinaryOperator::And,
            right,
        } => extract_correlated_eq(left).or_else(|| extract_correlated_eq(right)),
        Expr::Nested(inner) => extract_correlated_eq(inner),
        _ => None,
    }
}

/// Extract table.column from a qualified identifier.
///