SQL：如何在SELECT中引用WHERE中的子表达式？

Question

一切！我有Postgresql和查询

SELECT
  complex_expression()
FROM
  t
WHERE
  complex_expression() != '';

有没有办法在查询中只编写一次complex_expression()然后再引用它？ Thanx提前

Answer 1

select * from
( 
SELECT complex_expression() ce
FROM t
)
where ce != '';