I *GAVE* you the answer to that. I *DID* create an index on userid
. *READ* what I said:
...but still putting an index on userid could well help the JOIN performance.
Even in the absence of a JOIN it will help.
But there is no point in putting an index on comments
if you are going to do
... AND comments LIKE '%like%' ...
because MySQL can't use an index with the LIKE operator.