Re: Convert Query from using Subqueries, compatible with MySQL 3.23

[Sean Nolan]

The example you gave can be rewritten (and should be) as a join.

select g.id, g.name, g.description, p.permission
from groups g left join permissions p on g.id=p.group_id or p.group_id Is Null
where p.id=3 or p.id is null;

In general, you can usually do away with subqueries by using joins, joins with group by, or by creating a temporary table that you then join to the main query.

To create a temporary table, you can use this
CREATE TEMPORARY TABLE tempSubQuery SELECT ....
where the SELECT is pretty much the subquery (include the columns in the SELECT that will join to the main query).

Sean