Re: Golden Rules of writting efficient query

[KimSeong Loh]

> - Mysql use only one index for any query
MySQL uses 1 index for each table access, but in MySQL 5.0 it can use more than 1 index

> - avoid use of LIMIT
LIMIT is fine if used appropriately

> - use count(*) instead of count(field_name)
This 2 has different meaning in some situation

> - If WHERE is like "WHERE A = 200 OR B >1000" ,
> to optimize such query split query with UNION i.e
>
> "SELECT SOME_FIELDS FROM SOME_TABLE WHERE A =
> 200 UNION "SELECT * FROM SOME_TABLE WHERE B
> >1000" AND create separate index on field "A" and
> "B".
MySQL 5.0 may be able to use index merge optimization on this, but I am not so sure with the > , if both are = then it will.