Function check_join_is_valid 

pub fn check_join_is_valid(
    left: &Schema,
    right: &Schema,
    on: &[(Arc<dyn PhysicalExpr>, Arc<dyn PhysicalExpr>)],
) -> Result<(), DataFusionError>

Checks whether the schemas “left” and “right” and columns “on” represent a valid join. They are valid whenever their columns’ intersection equals the set on