When we try to do large table joins on varchar columns, we get an error of the form: ERROR: cannot perform local joins that involve expressions DETAIL: local joins can be performed between columns only

When we try to do large table joins on varchar columns, we get an error of the form: ERROR: cannot perform local joins that involve expressions DETAIL: local joins can be performed between columns only. This is because we have a check in CheckJoinBetweenColumns() which requires the join clause to have only 'Var' nodes (i.e. columns). Postgres adds a relabel type cast to cast the varchar to text; hence the type of the node is not T_Var and the join fails.