hi,
can anyone please tell me how a secondary index can be deemed as effective?
i did trace for a user and the EXPLAIN shows:
Image may be NSFW.
Clik here to view.
Now after running index advisor and doing another EXPLAIN including the recommended secondary index, the new EXPLAIN shows:
Image may be NSFW.
Clik here to view.
Since the "Estimated Costs" (high-lighted in yellow) did not actually improve, this means that the recommended secondary index is not effective. Is my assumption correct? If not, how do I know if a secondary index is effective?
Thank you.
