[
https://issues.apache.org/jira/browse/DERBY-6569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14001534#comment-14001534
]
Knut Anders Hatlen commented on DERBY-6569:
-------------------------------------------
Yes, I'm inclined to agree that it's a bug. Although some might call it an
extension. And to further complicate things: CREATE FUNCTION didn't get support
for the DETERMINISTIC keyword until Derby 10.5 (DERBY-3570), so all functions
created by old applications are implicitly declared non-deterministic.
If we forbid non-deterministic function calls in NULLIF, as the standard
requires, we should have a release note that tells users to rewrite affected
applications either by redeclaring functions as deterministic if that's what
they really are, or by restructuring their query so that the non-deterministic
expression is not contained in the NULLIF expression. For example, the
problematic expression in the issue description could be rewritten from
{{SELECT NULLIF(INT(RANDOM()*2), 1) FROM SYS.SYSTABLES}} to {{SELECT NULLIF(R,
1) FROM (SELECT INT(RANDOM()*2) FROM SYS.SYSTABLES) S(R)}}.
We could do that. I'm just a little worried about the backward compatibility
given that all functions created with Derby 10.4 and earlier will be disallowed
in NULLIF and require application changes.
> NULLIF may return incorrect results if first operand calls non-deterministic
> function
> -------------------------------------------------------------------------------------
>
> Key: DERBY-6569
> URL: https://issues.apache.org/jira/browse/DERBY-6569
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.10.2.0
> Reporter: Knut Anders Hatlen
> Assignee: Knut Anders Hatlen
> Attachments: d6569-1a.diff
>
>
> The SQL standard doesn't allow non-deterministic function calls in the
> operands of NULLIF. Derby does however allow such calls, but the results may
> not be as one might expect.
> Take an expression such as NULLIF(expr, 1). It shouldn't ever return 1. If
> expr is 1, it should return NULL, and if expr is not 1, it should return expr.
> If expr contains a call to a non-deterministic function, it may actually end
> up returning 1 sometimes:
> {noformat}
> ij> SELECT NULLIF(INT(RANDOM()*2), 1) FROM SYS.SYSTABLES;
> 1
> -----------
> 1
> 1
> 1
> NULL
> NULL
> NULL
> NULL
> 0
> 1
> NULL
> NULL
> 0
> 0
> NULL
> 0
> 1
> 0
> NULL
> 1
> 0
> NULL
> NULL
> NULL
> 23 rows selected
> {noformat}
--
This message was sent by Atlassian JIRA
(v6.2#6252)
