I have an index that shows distribution statistics of 98.20%, which is very poor. I set show query plan and show statis I/O on. This table has 1113675 rows of data.

*************
select orderID, custId, intertcsi from tblorders
where intertcsi = '2815'

STEP 1
The type of query is SELECT
FROM TABLE
tblorders
Nested iteration
Index : indxInterTCSI
orderID custId intertcsi
----------- ----------- ---------
1015245 1011313 2815
2556392 2556392 2815
2537264 2537264 2815
...
Table: tblOrders scan count 1, logical reads: 104, physical reads: 58, read ahead reads: 0
**************
Then I use the same select statement to force a table scan:

select orderID, custId, intertcsi from tblorders (index=0)
where intertcsi = '2815'

STEP 1
The type of query is SELECT
FROM TABLE
tblorders
Nested iteration
Table Scan
orderID custId intertcsi
----------- ----------- ---------
60472 61084 2815
102184 102333 2815
...
Table: tblOrders scan count 1, logical reads: 110795, physical reads: 6891, read ahead reads: 103980
When the index is not provided, the logical reads and physical reads increased dramatically.
Does this tell me that I should keep that index though it is a poor selection? Is that because a huge table
like this make the optimizer use the index despite indication of distribution statistiics? The query without using
index takes longer time to run.
Any of your idea or comment would be very appreciated.
Thanks for the sites provided.
Su Ge