[jira] [Updated] (DERBY-6569) NULLIF may return incorrect results if first operand calls non-deterministic function

["Knut Anders Hatlen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DERBY-6569?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Knut Anders Hatlen updated DERBY-6569:
--------------------------------------
    Attachment: d6569-1b.diff

DERBY-1576 added the CachedValueNode class to help prevent multiple evaluations of an expression. The updated patch [^d6569-1b.diff] wraps the left operand of the NULLIF expression in such a node. All tests ran cleanly with the patch.

Even though the standard doesn't allow non-deterministic expressions in a NULLIF expression, I don't think we will enforce that limitation because of the previously discussed backward compatibility implications. I intend to check in this patch so that we at least don't get confusing/unexpected results if NULLIF is used on non-deterministic expressions.

> 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, d6569-1b.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}



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