Package io.trino.sql.planner.iterative.rule

Class ImplementExceptDistinctAsUnion

  • All Implemented Interfaces:
    Rule<ExceptNode>
    public class ImplementExceptDistinctAsUnion
extends Object
implements Rule<ExceptNode>
    Converts EXCEPT DISTINCT queries into UNION ALL..GROUP BY...WHERE E.g.: 
         SELECT a FROM foo
     EXCEPT DISTINCT
     SELECT x FROM bar
    => 
         SELECT a
     FROM
     (
         SELECT a,
         COUNT(foo_marker) AS foo_count,
         COUNT(bar_marker) AS bar_count
         FROM
         (
             SELECT a, true as foo_marker, null as bar_marker
             FROM foo
             UNION ALL
             SELECT x, null as foo_marker, true as bar_marker
             FROM bar
         ) T1
     GROUP BY a
     ) T2
     WHERE foo_count >= 1 AND bar_count = 0;