如何在SELECT中消除重复的大小写或多次解码语句

Question

例如:

SELECT a,
  IF (c = DECODE(b, "foo1", "bar1", "foo2", "bar2") THEN c ELSE 0),
  IF (d != DECODE(b, "foo1", "bar1", "foo2", "bar2") THEN d ELSE 2),
  IF (e = DECODE(b, "foo1", "bar1", "foo2", "bar2") THEN e ELSE 5)
FROM x

似乎应该有一种更少重复的方法来做到这一点…

Answer 1

use

SELECT 
a,
IF (c = b THEN c ELSE 0),
IF (d != b THEN d ELSE 2),
IF (e = b THEN e ELSE 5)
FROM
(SELECT a, DECODE(b, "foo1", "bar1", "foo2", "bar2") b, c, d, e from x);

Answer 2

SELECT a,
  DECODE( c, b_decoded, c, 0 ),
  DECODE( d, b_decoded, 2, d ),
  DECODE( e, b_decoded, e, 5 )
FROM (SELECT a, c, d, e, DECODE(b, "foo1", "bar1", "foo2", "bar2") b_decoded FROM x)