[jira] Commented: (DERBY-4513) Forbid NEXT VALUE FOR clause in certain contexts

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

    [ https://issues.apache.org/jira/browse/DERBY-4513?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12799675#action_12799675 ] 

Knut Anders Hatlen commented on DERBY-4513:
-------------------------------------------

Hi Rick,

I'm fine with extra restrictions in the initial implementation, but I'm afraid I didn't understand exactly what limitation you're suggesting. Are you suggesting to limit the number of NEXT VALUE FOR clauses per row or per statement?

> Forbid NEXT VALUE FOR clause in certain contexts
> ------------------------------------------------
>
>                 Key: DERBY-4513
>                 URL: https://issues.apache.org/jira/browse/DERBY-4513
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.6.0.0
>            Reporter: Rick Hillegas
>
> This is part of the work needed to implement ANSI/ISO sequences. The functional spec attached to DERBY-712 lists various situations in which the NEXT VALUE FOR clause is illegal. These include:
>     * CASE expression
>     * WHERE clause
>     * ORDER BY clause
>     * AGGREGATE expression
>     * WINDOW function
>     * DISTINCT select list
> In addition, I propose that we make it illegal for a statement to have more than one NEXT VALUE FOR clause on the same sequence generator. This is a tighter restriction than the ANSI/ISO standard calls for. The standard requires that if two columns in a row are populated by NEXT VALUE FOR clauses on the same sequence, then the values should be the same. I don't feel confident that I could track down all of the cases which could give rise to this situation--so I propose to limit the number of NEXT VALUE FOR clauses on a given sequence generator to just 1.

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