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https://issues.apache.org/jira/browse/DERBY-4371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901435#action_12901435
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Knut Anders Hatlen commented on DERBY-4371:
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Thanks Nirmal, the new patch was easier to read. And thanks for adding all the
test cases.
I believe the code is correct, but it's still somewhat tricky to understand,
especially because of the nesting levels and the way it breaks out of the
loops. Here are some suggestions that I think would make the code easier to
follow:
1) Reduce the nesting level in the else branch in bindOrderByColumn(). Instead
of the current code with two levels
if (addedColumnOffset >= 0 && ....) {
if (!expressionMatch(target)) {
merge them into one if statement:
if (addedColumnOffset >= 0 && ....
&& !expressionMatch(target)) {
2. Instead of breaking out of the loop in bindOrderByColumn() with the "break"
keyword when a non-matching column is found, just throw the exception
immediately. Then it's easier to see what the effect of a mismatch is.
3. Given that the "throw" statement is moved inside the loop as part of comment
(2), there's no need to check explicitly whether the list of collected nodes
was empty, so "if(collectNodesVisitor.getList().isEmpty())" can be removed.
4. The results of some sub-expressions could be put in to local variables to
avoid having to repeat them. For example, target.getResultColumns() in
expressionMatch(), and target.getResultColumns() and
target.getResultColumns().getResultColumn(i).getExpression() in
columnMatchFound().
5. The loop in columnMatchFound() could be simplified by returning true
immediately when a match is found, instead of setting a flag and then checking
the flag further down in the loop body.
> 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
> Assignee: C.S. Nirmal J. Fernando
> Priority: Critical
> Attachments: DERBY-4371-2.diff, DERBY-4371-3.diff, DERBY-4371-4.diff,
> derby-4371-5.diff, derby-4371-6.diff, derby-4371-tests.diff, DERBY-4371.diff
>
>
> 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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