Jesus Camacho Rodriguez created HIVE10770:

Summary: Recognize additional common factors in Filter predicates
Key: HIVE10770
URL: https://issues.apache.org/jira/browse/HIVE10770
Project: Hive
Issue Type: Bug
Reporter: Jesus Camacho Rodriguez
Assignee: Jesus Camacho Rodriguez
Currently, we canonize predicates at the term level (i.e. "a or b or a" becomes "a or b" but
we do not attempt to recognize terms that are equivalent). Further, we do not exploit e.g.
the symmetry of '=' (i.e. a = b iff b = a).
 A first extension would be to normalize comparisons between field references and literals
so that the lower field reference is always on the left. So, "$6 = $3" becomes "$3 = $6";
"$6 > $3" becomes "$3< $6". And "literal <= $5" becomes "$5 >= literal". This
would not damage performance, and would improve a few plans.
 Another possible extension. Given the predicate "(a or b) and ((x and a) or (y and b))",
the first factor can be removed so the expression consists only of "(x and a) or (y and b)".
One possible way to recognize such cases is to transform the second factor to CNF i.e. "(x
or y) and (x or b) and (a or y) and (a or b)", and as it contains "(a or b)", we would know
that we can discard it. Then we could just use the original expression i.e. "(x and a) or
(y and b)" in the predicate, once we have done the check.

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