Order by in subselect

Question

Hello,
when using a ORDER BY clause in a subquery, i get the following error:
Error -
Auto Commit: On, SQL Mode: Internal, Isolation Level: Committed
General error;-5016 POS(286) Missing delimiter: )
SELECT *
     FROM DOCPROTOCOL D
     WHERE D.DOCID = (
                              SELECT DP.DOCID
                              FROM DOCPROTOCOL  DP
                              WHERE DP.DOCID = 5
                              AND DP.ACTIONSYM=10
                              ORDER BY DP.XTIME  ASC
                              LIMIT 1
The "ORDER"-Keyword is marked.
Trying the same request without the order-by part works fine, but naturally returns something different - which is not the result I want.
(I know, that the above sample is kind of useless -  the "real" statement is more complex, so I tried to reduce it to a minimum.)
Are ORDER BY's not supported in subqueries? If so, are there any alternatives? Or did I overlook something?
Thanks in advance.

Answer 1

nobodyknows wrote:>
> Hello,
>
> when using a ORDER BY clause in a subquery, i get the following error:
>
> -
Error -
> Auto Commit: On, SQL Mode: Internal, Isolation Level: Committed
>  General error;-5016 POS(286) Missing delimiter: )
> SELECT *
>      FROM DOCPROTOCOL D
>      WHERE D.DOCID = (
>                               SELECT DP.DOCID
>                               FROM DOCPROTOCOL  DP
>                               WHERE DP.DOCID = 5
>                               AND DP.ACTIONSYM=10
>                               ORDER BY DP.XTIME  ASC
>                               LIMIT 1
>                        )
>
> The "ORDER"-Keyword is marked.
> Trying the same request without the order-by part works fine, but naturally returns something different - which is not the result I want.
> (I know, that the above sample is kind of useless -  the "real" statement is more complex, so I tried to reduce it to a minimum.)
>
> Are ORDER BY's not supported in subqueries? If so, are there any alternatives? Or did I overlook something?
No ORDER BY in subqueries aren't supported.
From what I see in your example something like this should work even better:
SELECT *
     FROM DOCPROTOCOL D
     WHERE D.DOCID = (
                              SELECT max(DP.DOCID)
                              FROM DOCPROTOCOL  DP
                              WHERE DP.DOCID = 5
                              AND DP.ACTIONSYM=10
This is better because:
- it makes clear what you want to do
- it prevents useless sort operations
- it enables max/min optimizations if the DOCID is a indexed field or key column
regards,
Lars