Reuse Subquery from Select Expression in WHERE-Clause

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?
• St开发者_StackOverflowored Function?
• HAVING?
• other?

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'