Function extract_join_predicate

nodedb-sql/src/planner/dml_update_delete.rs:183–220

Extract a single equi-join predicate of the form `target_table.col = source_table.col` (or the reverse) from a WHERE expression, returning `(target_col, source_col, remaining_filters)`. Also accepts `col = other_table.col` where `col` without a table qualifier is assumed to belong to the target (PostgreSQL behavior).

(
    expr: &ast::Expr,
    target_ref: &str,
    source_ref: &str,
)

/// Also accepts `col = other_table.col` where `col` without a table qualifier is
/// assumed to belong to the target (PostgreSQL behavior).
fn extract_join_predicate(
    expr: &ast::Expr,
    target_ref: &str,
    source_ref: &str,
) -> Result<(String, String, Vec<Filter>)> {
    // Flatten the top-level AND chain.
    let mut conjuncts: Vec<ast::Expr> = Vec::new();
    flatten_and_expr(expr, &mut conjuncts);

    // Find the first conjunct that is an equi-join between target and source.
    let mut join_idx: Option<usize> = None;
    let mut target_col = String::new();
    let mut source_col = String::new();

    for (i, conjunct) in conjuncts.iter().enumerate() {
        if let Some((tc, sc)) = try_equijoin_pair(conjunct, target_ref, source_ref) {
            target_col = tc;
            source_col = sc;
            join_idx = Some(i);
            break;
        }
    }

    let join_idx = join_idx.ok_or_else(|| SqlError::Parse {
        detail: format!(
            "UPDATE ... FROM requires a WHERE clause equi-join predicate of the form \
             `{target_ref}.col = {source_ref}.col`; none found"
        ),
    })?;

    conjuncts.remove(join_idx);

    // Remaining conjuncts become target_filters. Strip table qualifier so
    // `uf_target.score` becomes `score` — documents store bare field names.
    let target_filters = strip_and_convert_filters(conjuncts, target_ref)?;

    Ok((target_col, source_col, target_filters))
}

/// Try to extract `(target_col, source_col)` from an equality expression
/// where one side is `target_ref.col` and the other is `source_ref.col`.