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Is it right to have more than one INDEX key for the same column in MySQL database?
for example, id field indexed twice with different Keyname while phpmyadmin gives me a warning message:
More than one INDEX key was created
for columnid
I would like to know if that is ok, and if there are any effects or side-effect on my script or the server using this method?
I use this method for grouping columns for each index.
Indexing a single column twice is useless, slows down inserts and updates because now you have to (uselessly) maintain two indexes, and probably confuses the optimizer (if it doesn’t actually break something). On the other hand, it’s fine (and often useful) to have a column indexed alone and then also as part of one or more compound keys.