Hi,
I don't want it to count the rows with col1 as null. When I specify
col1=col2, I am implicitly saying that they are both non-null and equal to
each other.
regards,
ram
-----Original Message-----
Sent: Friday, March 30, 2001 6:25 PM
To: Multiple recipients of list ORACLE-L
Well, how will it count the rows where col1 is null if it just uses the
index? There are no entries in the index for those rows...
>>> [EMAIL PROTECTED] 03/30/01 06:30AM >>>
> Hi,
> I have a table A with two identical, integer, nullable columns col1 and
> col2, both of which are indexed.
> The table A has 100,000 rows and takes up 11,000 blocks.
> The indexes on the two columns take about 225 leaf blocks each with
> BLevel=1.
> The optimizer goal is set to CHOOSE and the table analyzed with compute
> stats.
> Oracle version 8.1.7 on Win' 2000.
>
> Right, when I now run the query:
>
> SELECT COUNT(col1)
> FROM A
> WHERE col1=col2;
>
> the CBO is doing a full table scan on A (with 11000 physical reads)
> rather than just joining
> the two indexes to get the result.
>
> I have two questions:
> 1. Why is the CBO not choosing to join the indexes by default?
> 2. When I gave an INDEX_JOIN hint
> /*+ INDEX_JOIN (A COL1IDX COL2IDX) */,
> it did do a hash join of the two indexes which was faster but still
> took about 6500 physical
> reads while the two indexes put together take only about 452
> blocks. Any idea what the
> extra disk reads are doing?
>
> Thanks in advance,
> Ram
>
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