which table index is used while actual running
How do I know that which index is used by the sql query to know whether index is degrading the performance or not at all used.
Siegfried Boes replied
I would not really say, that ther primary index is used by default, it is possible that no index is used at all (full table scan, which is better if more than 10% of the table come back)
Which index is used is determined by the total selectivity of the index (check index fields from the first whether they are in the WHERE condition with an equal, selectivity is 1/ (number of different values), see also postings above. Index with highest selectivity is used.
More about SQL trace can be found here:
See last section about the explain, the explain tells you which index is used.