如何在基础的select-join语句中使用create table语句的列别名？

Question

I've run into a minor problem with a query I want to build. The idea is to construct a new table based on a join on the same old table where some kind of "expensive" calculation is done.

The problem

I can not use the calculated result (alias) of the field list in the where (or on) clause of the underlying select.

Why not calculate it again?

• I would like to avoid calculating the result again as it is a 1.5 Mio entry table and I join about everything. There are some more conditions in the on clause but it's not really making a difference in number of operations. Therefore I'd rather not do it twice per join.
• I just wanna now if it is possible :)

SQL Statement

CREATE TABLE `newTable` AS (
    SELECT (*COMPUTATION*) AS `calculated` 
    FROM oldTable AS t1 
    JOIN oldTable as t2 ON (
        t1.user != t2.user
        AND *other conditions*
    )
    WHERE `calculated` < *some number*
);

I've already thought of using functions or something else, but I think it should be doable in one simple query.

Answer 1

Have you tried wrapping your inner query one more level??

CREATE TABLE `newTable` AS 
(   select PreQuery.Calculated
       from ( SELECT (*COMPUTATION*) AS `calculated` 
                 FROM oldTable AS t1 
                 JOIN oldTable as t2 ON 
                   ( t1.user != t2.user
                     AND *other conditions* 
                   ) ) PreQuery
       where PreQuery.Calculated < *some number*
);