Details
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Bug
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Status: Open
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Minor
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Resolution: Unresolved
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Impala 3.1.0
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None
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None
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ghx-label-4
Description
Consider the existing unit test: ExprRewriteRulesTest.TestNormalizeBinaryPredicatesRule, with this SELECT expression:
cast(0 as double) = id
The existing test case simply does a "toSql" on the rewritten expression, suppressing implicit casts, expecting:
id = CAST(0 AS DOUBLE)
However, if we examine the AST itself, or render the rewritten expression showing implicit casts, we see we get:
CAST(id AS DOUBLE) = CAST(CAST(0 AS DOUBLE) AS DOUBLE)
In this particular case, the double-case it benign as the constant-folding rule, if enabled, will remove the two casts. But, if the value were a column, the double casts would exist in the plan sent to the, resulting in an unnecessary extra step.
The expected behavior is the function argument type propagation would not insert a cast if it is not needed.
Researching a bit more, it seems this is an artifact of recent changes in toSql(). In the NumericLiteral, we always display the type as a cast. The query specified a cast also, so the outer cast comes from the original SQL, the inner from pushing the cast type into the numeric literal.
This is not so much a bug as it is a muddling of the semantics. There is no reason to push the type into the numeric literal if an explicit cast exists.