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

Class ImplementExceptDistinctAsUnion

java.lang.Object
io.trino.sql.planner.iterative.rule.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;