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https://issues.apache.org/jira/browse/DERBY-6408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13906879#comment-13906879
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Knut Anders Hatlen commented on DERBY-6408:
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I think the syntax is not supported in 10.6 and earlier because the boolean
data type was not introduced until 10.7. EXISTS returns a boolean.
> EXISTS returns NULL instead of FALSE
> ------------------------------------
>
> Key: DERBY-6408
> URL: https://issues.apache.org/jira/browse/DERBY-6408
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.7.1.1, 10.8.3.3, 10.9.2.2, 10.10.1.1
> Reporter: Knut Anders Hatlen
>
> The reference manual topic on Boolean expressions -
> http://db.apache.org/derby/docs/10.10/ref/rrefsqlj23075.html - says that
> EXISTS should return FALSE if the subquery returns no rows. In reality, it
> returns NULL:
> ij> create table t(x int);
> 0 rows inserted/updated/deleted
> ij> values exists(select * from t);
> 1
> -----
> NULL
> 1 row selected
> SQL:2011, part 2, 8.10 <exists predicate> also says that FALSE is the correct
> result if the cardinality is 0.
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