Function mz_sql::plan::query::plan_order_by_or_distinct_expr

source · 
fn plan_order_by_or_distinct_expr(
    ecx: &ExprContext<'_>,
    expr: &Expr<Aug>,
    output_columns: &[(usize, &ColumnName)],
) -> Result<HirScalarExpr, PlanError>
Expand description

Plans an expression that appears in an ORDER BY or DISTINCT ON clause.

The output_columns parameter describes, in order, the physical index and name of each expression in the SELECT list. For example, [(3, "a")] corresponds to a SELECT list with a single entry named “a” that can be found at index 3 in the underlying relation expression.

There are three cases to handle.

  1. A simple numeric literal, as in ORDER BY 1. This is an ordinal reference to the specified output column.
  2. An unqualified identifier, as in ORDER BY a. This is a reference to an output column, if it exists; otherwise it is a reference to an input column.
  3. An arbitrary expression, as in ORDER BY -a. Column references in arbitrary expressions exclusively refer to input columns, never output columns.