Function resolve_grouping_expression 

pub fn resolve_grouping_expression<'a>(
    routines: &dyn RoutineResolution,
    expression: &'a ScalarExpr,
    projections: &'a [ProjectionPlan],
    schema: &RowSchema,
    outer: Option<&RowSchema>,
    params: &[SQLParam],
) -> Result<Cow<'a, ScalarExpr>, SQLError>

An unqualified input column wins even when its lookup is ambiguous. Output names are considered only for a whole bare name, never inside an expression. schema holds the query’s own columns over outer, the scope of the queries that enclose it, whose columns do not take a name before an output column.