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https://issues.apache.org/jira/browse/CALCITE-2921?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16899786#comment-16899786
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Danny Chan commented on CALCITE-2921:
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Thanks, in CALCITE-2302, for NULLIF(NULL, y), it did not support deduce the
NULL type because its operands type checker is null, but we can do that because
we know the type of y, i can do if this is required; for AVG(NULL), we would
deduce the NULL to be type decimal(with default precision/scale) because we
already declare that the operand need to be of type family NUMERIC(i have
defined the default type for every SqlTypeFamily in CALCITE-2302).
For the null literal plan improvements, i'm + 1 with the way you fix.
> Allow NULL as argument to function calls
> ----------------------------------------
>
> Key: CALCITE-2921
> URL: https://issues.apache.org/jira/browse/CALCITE-2921
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.18.0
> Reporter: pengzhiwei
> Assignee: Julian Hyde
> Priority: Critical
> Labels: pull-request-available
> Fix For: 1.21.0
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> Currently {{nullif(null,y)}} throws exception in verification. This is
> because translates {{nullif(x,y)}} to a case-when expression, just like "case
> when x = y then null else x". So when "x" is null literal,a exception throws
> out as follow:
> {code:java}
> ELSE clause or at least one THEN clause must be non-NULL
> {code}
> I have test in mysql,"nullif(null,y) works well.So I think we should allow
> this usage of "nullif".
> There are two ways to fix this issue:
> 1) Skip the check for "foundNotNull" in SqlCaseOperator#checkOperandTypes:
>
> {code:java}
> if (!foundNotNull) {
> // according to the sql standard we can not have all of the THEN
> // statements and the ELSE returning null
> if (throwOnFailure) {
> throw callBinding.newError(RESOURCE.mustNotNullInElse());
> }
> return false;
> }{code}
> However, as the comment says, we cannot have all of the THEN and ELSE
> returning null.
> 2) Disable the translation from nullif to case-when and keep "nullif" as it
> is.
> Any suggestion is welcomed,Thanks!
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