Reuse Subquery from Select Expression in WHERE-Clause

问题

Of course it isn't possible to write

SELECT (some subselect) AS blah FROM t WHERE blah = 'const'

What is the best way to do this?

• SELECT (some subselect) FROM t WHERE (some subselect) = 'const'?
• View?
• Stored Function?
• HAVING?
• other?

回答1:

you can move (some subselect) as table in the FROM :

SELECT s.blah
  FROM t, (some subselect) s
 WHERE t.id = s.id
   AND s.blah = 'const'

来源：https://stackoverflow.com/questions/5720983/reuse-subquery-from-select-expression-in-where-clause