You should try, if you can, to avoid expressions in Selects, such as SELECT ColumnA +
ColumnB, etc. The query optimizer of the database, the portion of the DBMS that determines the best way to get the required data out of the database itself, handles expressions in such a way that would normally require more time to retrieve the data than if columns were normally selected, and the expression itself handled programmatically.
Minimize the number of columns included in a Group By clause.
If you are using a join, try to have the columns joined on (from both tables) indexed.
When in doubt, index.
Unless doing multiple counts or a complex query, use COUNT(*) (the number of rows
generated by the query) rather than COUNT(Column_Name)
