Function join_allows_pushdown

pub fn join_allows_pushdown(
    projection_as_columns: &[(Column, String)],
    join_schema: &Arc<Schema>,
    far_right_left_col_ind: i32,
    far_left_right_col_ind: i32,
) -> bool

Checks three conditions for pushing a projection down through a join:

• Projection must narrow the join output schema.
• Columns coming from left/right tables must be collected at the left/right sides of the output table.
• Left or right table is not lost after the projection.