James Taylor created PHOENIX-3489:
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Summary: Compile out expressions formed by only columns with WHERE
clause equality constraints in GROUP BY and ORDER BY
Key: PHOENIX-3489
URL: https://issues.apache.org/jira/browse/PHOENIX-3489
Project: Phoenix
Issue Type: Bug
Reporter: James Taylor
Since columns constrained by equality constraints evaluate to the same constant
value, expressions formed only by them may be stripped out of GROUP BY and
ORDER BY clauses.
For example, the group by key for this query can be only pk2:
{code}
SELECT FLOOR(pk1), pk2 FROM t WHERE pk1 = 1
GROUP BY FLOOR(pk1), pk2
{code}
This can be implemented by
- using OrderPreservingTracker.IsConstantVisitor to detect this case
- evaluating the expression at compilation time
- storing the resulting LiteralExpression as the leading group by expressions
- storing the count of constant expressions in GroupBy as constantGroupByCount
- modifying ExpressionCompiler.wrapGroupByExpression() to return the
LiteralExpression when the position is less that the constantGroupByCount
- sending to the server only non constants in the GroupBy.keyExpressions list
For ORDER BY, we can simply remove these expressions from the
OrderBy.orderByExpressions lists. A further optimization would be to not even
project the constant ORDER BY expression and transform it into a literal on the
client side.
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