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https://issues.apache.org/jira/browse/OPENJPA-1483?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Fay Wang resolved OPENJPA-1483.
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Resolution: Fixed
> count (Distinct e) in JPQL gives wrong result when the id field is a compound
> primary key
> -----------------------------------------------------------------------------------------
>
> Key: OPENJPA-1483
> URL: https://issues.apache.org/jira/browse/OPENJPA-1483
> Project: OpenJPA
> Issue Type: Bug
> Affects Versions: 2.1.0
> Reporter: Fay Wang
> Fix For: 2.1.0
>
> Attachments: OPENJPA-1483-2.patch, OPENJPA-1483.patch
>
>
> This is a fundamental problem with count when compound primary key is
> involved.
> (1) If no relation navigation is involved:
> String jpql = "SELECT COUNT (DISTINCT e) FROM G2 e";
> With the property below:
> <property name="openjpa.jdbc.DBDictionary"
> value="db2(useWildCardForCount=true)" />
> Openjpa will generate the following sql and return the correct count:
> SELECT COUNT(*) FROM G2 t0 optimize for 1 row
> (2) If there is relation navigation invloved:
> String jpql = "SELECT COUNT (DISTINCT f1.g2) FROM F1 f1";
>
> The property of useWildCardForCount will not generate correct sql with
> right result. However, given the object-relational impedance mismatch, there
> is no corresponding SQL construct for count of multiple primary keys, and
> there is no clean and generic solution to solve this problem. The only
> workaround is to use native SQL with table expression:
> SELECT COUNT(*)
> FROM (SELECT DISTINCT G1.G1PK, G1.G2PK FROM F1 t0 INNER JOIN G2 t1 ON
> t0.G1PK = t1.G1PK AND t0.G2PK = t1.G2PK)) TX;
> Rather than giving a wrong answer, OpenJPA should give an Unsupported
> exception.
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