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From "Yan Zhou (JIRA)" <j...@apache.org>
Subject [jira] Created: (PIG-1635) Logical simplifier does not simplify away constants under AND and OR; after simplificaion the ordering of operands of AND and OR may get changed
Date Tue, 21 Sep 2010 15:36:34 GMT
Logical simplifier does not simplify away constants under AND and OR; after simplificaion the
ordering of operands of AND and OR may get changed
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                 Key: PIG-1635
                 URL: https://issues.apache.org/jira/browse/PIG-1635
             Project: Pig
          Issue Type: Bug
          Components: impl
            Reporter: Yan Zhou
            Assignee: Yan Zhou
            Priority: Minor


b = FILTER a by (( f1 > 1) AND (1 == 1))

or 

b = FILTER a by ((f1 > 1) OR ( 1==0))

should be simplified to

b = FILTER a by f1 > 1;

Regarding ordering change, an example is that 

b = filter a by ((f1 is not null) AND (f2 is not null));

Even without possible simplification, the expression is changed to

b = filter a by ((f2 is not null) AND (f1 is not null));

Even though the ordering change in this case, and probably in most other cases, does not create
any difference, but for two reasons some users might care about the ordering: if stateful
UDFs are used as operands of AND or OR; and if the ordering is intended by the application
designer to maximize the chances to shortcut the composite boolean evaluation. 

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