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https://issues.apache.org/jira/browse/DERBY-5613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13208017#comment-13208017
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Mamta A. Satoor commented on DERBY-5613:
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But we haven't qualified the country column with the left table or right table.
Instead it is a join column which as per SQL spec should be replaced by
COALESCE, I haven't looked at the spec in detail on this, but if country in
SELECT is to be replaced with COALESCE(COUNTRIES.county, CITIES.country), then
should we be allowing join column country in SELECT to be bound to the
COUNTRIES table? When we decide to work on this issue, we probably should look
into SQL spec more about the expected behavior for such a query.
If the query above was rewritten to have group by on CITIES.country, the query
would fail because that column is not in the SELECT list.
SELECT country,count(country) FROM COUNTRIES JOIN CITIES USING (COUNTRY) group
by CITIES.country
Currently, in Derby (based on my work on DERBY-4631), for a LEFT OUTER JOIN and
INNER JOIN with USING/NATURAL, the join column in the SELECT list gets bound to
the left table. For RIGHT OUTER JOIN with USING/NATURAL, the join column in the
SELECT list gets bound to the right table. Based on what we find in the SQL
spec, this binding logic for the join columns may or may not be correct.
> Queries with group by column not included in the column list for JOIN(INNER
> or OUTER) with NATURAL or USING does not fail
> -------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-5613
> URL: https://issues.apache.org/jira/browse/DERBY-5613
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.8.2.2
> Reporter: Mamta A. Satoor
>
> A query like following does not raise an error even though countries.country
> is not part of the SELECT column list.
> SELECT country,count(country) FROM
> COUNTRIES JOIN CITIES USING (COUNTRY) group by countries.country
> This jira is related to DERBY-4631. As noted by Knut in DERBY-4631, SQL:2003
> says that the join columns in a natural join or in a named columns join
> should be added to the select list by coalescing the column from the left
> table with the column from the right table.
> Section 7.7, <joined table>, syntax rules:
> > 1) Let TR1 be the first <table reference>, and let TR2 be the <table
> > reference> or <table factor> that is the second operand of the
> > <joined table>. Let RT1 and RT2 be the row types of TR1 and TR2,
> > respectively. Let TA and TB be the range variables of TR1 and TR2,
> > respectively. (...)
> and
> > 7) If NATURAL is specified or if a <join specification> immediately
> > containing a <named columns join> is specified, then:
> (...)
> > d) If there is at least one corresponding join column, then let SLCC
> > be a <select list> of <derived column>s of the form
> >
> > COALESCE ( TA.C, TB.C ) AS C
> >
> > for every column C that is a corresponding join column, taken in
> > order of their ordinal positions in RT1.
> Derby has it's on logic to retrieve the join column values. It always picks
> up join column's value from the left table when we are working with natural
> left outer join and it picks up the join column's value from the right table
> when we are working with natural right outer join. But this logic does not
> work for all cases for right outer join. The fix being worked for DERBY-4631
> is to pick the join column's value based on following logic
> 1)if the left table's column value is null then pick up the right table's
> column's value.
> 2)If the left table's column value is non-null, then pick up that value
> Although this new logic will in essence implement what adding a COALESCE
> function for a join colunm might have done but it still allows following
> query to compile and run
> SELECT country,count(country) FROM
> COUNTRIES JOIN CITIES USING (COUNTRY) group by countries.country
> I think query above succeeds because in case of an INNER JOIN or LEFT OUTER
> JOIN, Derby associates the join column with the left table during it's bind
> phase. In case of RIGHT OUTER JOIN, Derby associates the join column with
> right table during it's bind phase. I believe, for these reasons, a query
> like above will not give an error for the group by column.
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