Package io.prestosql.sql.planner.iterative.rule

Class ImplementExceptAsUnion

java.lang.Object

io.prestosql.sql.planner.iterative.rule.ImplementExceptAsUnion

All Implemented Interfaces:

Rule<ExceptNode>

public class ImplementExceptAsUnion
extends Object
implements Rule<ExceptNode>

Converts EXCEPT queries into UNION ALL..GROUP BY...WHERE E.g.:

     SELECT a FROM foo
     EXCEPT
     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;
 

Nested Class Summary

Nested classes/interfaces inherited from interface io.prestosql.sql.planner.iterative.Rule

Rule.Context, Rule.Result

Constructor Summary

Constructors

Constructor	Description
ImplementExceptAsUnion(Metadata metadata)

Method Summary

Modifier and Type	Method	Description
Rule.Result	apply(ExceptNode node, Captures captures, Rule.Context context)
Pattern<ExceptNode>	getPattern()	Returns a pattern to which plan nodes this rule applies.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface io.prestosql.sql.planner.iterative.Rule

isEnabled

Constructor Detail

ImplementExceptAsUnion

public ImplementExceptAsUnion(Metadata metadata)

Method Detail

getPattern

public Pattern<ExceptNode> getPattern()

Description copied from interface: Rule

Returns a pattern to which plan nodes this rule applies.

Specified by:

getPattern in interface Rule<ExceptNode>

apply

public Rule.Result apply(ExceptNode node,
                         Captures captures,
                         Rule.Context context)

Specified by:

apply in interface Rule<ExceptNode>