Question

Below are the example query,How to add index with or clause ?

select fild1,fld2
  from tablename 
 where (field3='XXXX' or field4='YYYY') and field6='xdffgfd';

Will the below index work ?

ALTER TABLE tablename ADD INDEX ind_name(field3,field4,field6);

Answer 1

No. This is not a good indexing strategy. The compound index you suggest will work for the field3 lookup, but it cannot work for the field4 lookup.

You will need a separate index on field4 for that. If you provide a compound (field4, field6) index in addition to a (field3,field6) index you’ll optimize both parts of your OR clause for lookup, but you’ll incur an overhead on insertions and updates.