No.
The index should get used. The query result for query 2 is a subset of rows with ta.c1='val1' will get selected. Subset of query 1.
So there is no need for a full table scan. The index can be used in the following way :
1) Use index ind1 to get rows with ta.c1='val1' (which is query 1). This can definitely use an index.
2) Further filter using ta.c3 = 'val2'
Now may be the index is not very selective and the optimizer is going in for a full table scan. What is the cardinality like? It is strange that RULE or index hint is not taking it. Can you try a simple index(ta) hint or send your hint syntax. Can you try the hint on another table to make sure hint is working. I do not know why hint should not work.
Good luck.
"Daniel W. Fink" <Daniel.Fink@Sun.COM> wrote:
You answered your own question.
ta.c3 is a nonindexed column, this means that the only way to satisfy the
predicate is to perform a full table scan. Since this predicate condition forces
a full table scan on ta, which will retrieve the ta.c1 column values at the same
time, there is no need to use an index. In fact, an additional index access
would decrease the query performance.
Daniel Fink
bhabani s pradhan wrote:
> Hi All,
>
> Merry Christmas to all.
>
> I have this interesting problem..
>
> For this query index ind1 on (c1,c2) columns is getting used.
> SELECT 'x'
> FROM tab ta
> WHERE ta.c1='val1';
> (gives index ind1 range scan)
>
> But for
>
> SELECT 'x'
> FROM tab ta
> WHERE ta.c1='val1'
> AND ta.c3 = 'val2';
> (gives
FTS)
> index ind1 is not being used. c3 is a nonindexed column.
>
> I have already tried index(ta ind1) , RULE hints.
>
> The table and the index are analyzed.
>
> What cud be the reason for that?
>
> Regards,
> B S Pradhan
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Received on Wed Dec 24 2003 - 10:04:24 CST
