Paul Rogers created IMPALA-8000:
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Summary: Implied cast of NULL done for expressions, not literals
Key: IMPALA-8000
URL: https://issues.apache.org/jira/browse/IMPALA-8000
Project: IMPALA
Issue Type: Bug
Components: Frontend
Affects Versions: Impala 3.1.0
Reporter: Paul Rogers
Assignee: Paul Rogers
Impala can combine a cast with a null to create a typed null:
{noformat}
CAST(NULL AS SMALLINT) --> NULL:SMALLINT
{code}
Where the notation on the right indicates a NULL of type SMALLINT.
However, the analyzer appears to apply this optimization inconsistently. It is
done with constant folding:
{code:java}
String query = "SELECT 1 + NULL AS c" +
" from functional.alltypestiny";
AnalysisContext ctx = createAnalysisCtx();
ctx.getQueryOptions().setEnable_expr_rewrites(true);
SelectStmt select = (SelectStmt) AnalyzesOk(query, ctx);
Expr expr = select.getSelectList().getItems().get(0).getExpr();
assertEquals(ScalarType.SMALLINT, expr.getType());
assertTrue(expr instanceof NullLiteral);
{code}
But not for the near-identical result with an explicit cast:
{code:java}
String query = "SELECT CAST(NULL AS SMALLINT) AS c" +
" from functional.alltypestiny";
… // Same as above
assertEquals(ScalarType.SMALLINT, expr.getType());
// Fails, is actually CastExpr
//assertTrue(expr instanceof NullLiteral);
{code}
Interestingly, the NULL inside the CAST does have its type set to SMALLINT, so
the CAST is unnecessary.
Expected the analyzer to apply the rule consistently so that other rules don’t
have to handle both cases.
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