>> Thank you, I will try your method.
>> But it is strange. My original sql can be excuted while using sqlite
>> but not firebird.

My experience has been that all database products have different rules about what aliases can be
used in WHERE, GROUP BY, ORDER BY, and HAVING clauses. It seems to me that the most compatible
method is to repeat the entire expression. Some may allow aliases, original field names (but not
the alias you assigned to the field), column numbers, etc. in various parts, but not others. Some
will even refuse to let you use expressions, forcing you to wrap your statements in views just so
you can filter the results of the view. Good luck!

If you need cross-database solutions, make sure the group knows this when you ask for SQL help, so
we can try to avoid giving you FB-only solutions.

- Philip