|Subject||Re: [firebird-support] MAKE 'EXECUTE STATEMENT' USE INDEX|
Den 18.08.2015 16:59, skrev 'Mr. John' mr_johnmr@... [firebird-support]:
HI,in SP I have this queryWhy would you need an IIF condition? What about
FOR EXECUTE STATEMENT 'SELECT SUM(CANT) FROM TABLE1 WHERE FIEL1='||:F1||' AND FIEL2='||:F2|| IIF(:pCondition=1,' AND FIEL3='||:F3,'') INTO .. DO ..
TABLE1 PK =FIELD1,FIELD2,FIELD3
running the query gives a NATURAL PLAN
How to make it use the index?
Index is used if I change to:FOR SELECT SUM(CANT) FROM TABLE1 WHERE FIEL1=:F1 AND FIEL2=:F2 AND FIEL3=:F3 INTO .. DO ..
but this way I can't use the IIF condition that I need
FOR SELECT SUM(CANT) FROM TABLE1 WHERE FIEL1=:F1 AND FIEL2=:F2 AND (FIEL3=:F3 or cast(:pCondition as SmallInt) is distinct from 1) INTO .. DO ..
That could at least use an index for FIEL1 and FIEL2 (if they are the first two fields in your PK, that index could be used). Now, in some cases the index may have poor selectivity so that it still chooses natural (you didn't say whether "FOR SELECT SUM(CANT) FROM TABLE1 WHERE FIEL1=:F1 AND FIEL2=:F2 INTO .. DO .." uses an index or not). If so, the only way to use the index would be to use IF in your procedure and two separate queries, the index being used if you run the query comparing with FIEL3, but no index used when you run the query with only FIEL1 and FIEL2.
I've seen Dmitry Yemanov answer a different question (that may or may not be similar to yours) with repeating the first part and that could possibly translate to:
FOR SELECT SUM(CANT) FROM TABLE1 WHERE (FIEL1=:F1 AND FIEL2=:F2 AND FIEL3=:F3) or
(FIEL1=:F1 AND FIEL2=:F2 AND cast(:pCondition as SmallInt) is distinct from 1)
I never quite understood why I saw a similar statement to this, but I assume it doesn't hurt trying if my first suggestion fails.