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https://issues.apache.org/jira/browse/DERBY-4371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12764074#action_12764074
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Knut Anders Hatlen commented on DERBY-4371:
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SQL:2003 talks about this in part 2, 14.1 <declare cursor>, syntax rule 18d (18
d 9 B II, to be specific). My understanding is that if you have SELECT
DISTINCT, all the columns/expressions in the ORDER BY clause must also be found
in the select list.
Adding this restriction would solve the issue by rejecting the problematic
query. Whereas the behaviour of this particular query is not well-defined,
there may be some meaningful queries that will be rejected too, like "select
distinct i from t order by -i", so we should probably add a release note if we
choose to fix it this way.
Another data point, PostgreSQL does not allow any of the queries discussed here:
kh160127=# select distinct i from t order by j;
ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
kh160127=# select distinct i from t order by j*2;
ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
kh160127=# select distinct i from t order by -i;
ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
MySQL allows all three of them, although only the latter has a well-defined
ordering.
> Non-selected columns for SELECT DISTINCT allowed in ORDER BY clause if
> ordered by expression
> --------------------------------------------------------------------------------------------
>
> Key: DERBY-4371
> URL: https://issues.apache.org/jira/browse/DERBY-4371
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.5.1.1
> Reporter: Bernt M. Johnsen
> Priority: Critical
>
> How to repeat:
> ij> create table t (i integer, j integer);;
> 0 rows inserted/updated/deleted
> ij> insert into t values (1,2),(1,3);
> 2 rows inserted/updated/deleted
> ij> select distinct i from t order by j;
> ERROR 42879: The ORDER BY clause may not contain column 'J', since the query
> specifies DISTINCT and that column does not appear in the query result.
> ij> select distinct i from t order by j*2;
> I
> -----------
> 1
> 1
> 2 rows selected
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