Function plan_rows_from

src/sql/src/plan/query.rs:3082–3138

Plans a `ROWS FROM` expression. `ROWS FROM` concatenates table functions into a single table, filling in `NULL`s in places where one table function has fewer rows than another. We can achieve this by augmenting each table function with a row number, doing a `FULL JOIN` between each table function on the row number and eventually projecting away the row number columns. Concretely, the following qu

(
    qcx: &QueryContext,
    functions: &[Function<Aug>],
    alias: Option<&TableAlias>,
    with_ordinality: bool,
)

/// `with_ordinality` can be used to have the output expression contain a
/// single coalesced ordinality column at the end of the entire expression.
fn plan_rows_from(
    qcx: &QueryContext,
    functions: &[Function<Aug>],
    alias: Option<&TableAlias>,
    with_ordinality: bool,
) -> Result<(HirRelationExpr, Scope), PlanError> {
    // The `repeat_row` function is not supported in ROWS FROM.
    if functions.iter().any(is_repeat_row) {
        // Note: Would be also caught by WITH ORDINALITY checking for `repeat_row`, but then the
        // error message would be misleading, because it would refer to WITH ORDINALITY instead of
        // ROWS FROM.
        bail_unsupported!(format!("{} in ROWS FROM", REPEAT_ROW_NAME));
    }

    // If there's only a single table function, planning proceeds as if `ROWS
    // FROM` hadn't been written at all.
    if let [function] = functions {
        return plan_solitary_table_function(qcx, function, alias, with_ordinality);
    }

    // Per PostgreSQL, all scope items take the name of the first function
    // (unless aliased).
    // See: https://github.com/postgres/postgres/blob/639a86e36/src/backend/parser/parse_relation.c#L1701-L1705
    let (expr, mut scope, num_cols) = plan_rows_from_internal(
        qcx,
        functions,
        Some(functions[0].name.full_item_name().clone()),
    )?;

    // Columns tracks the set of columns we will keep in the projection.
    let mut columns = Vec::new();
    let mut offset = 0;
    // Retain table function's non-ordinality columns.
    for (idx, cols) in num_cols.into_iter().enumerate() {
        for i in 0..cols {
            columns.push(offset + i);
        }
        offset += cols + 1;

        // Remove the ordinality column from the scope, accounting for previous scope
        // changes from this loop.
        scope.items.remove(offset - idx - 1);
    }

    // If `WITH ORDINALITY` was specified, include the coalesced ordinality
    // column. Otherwise remove it from the scope.
    if with_ordinality {
        columns.push(offset);
    } else {
        scope.items.pop();
    }

    let expr = expr.project(columns);

    let scope = plan_table_alias(scope, alias)?;
    Ok((expr, scope))
}