Question

我正在进行级联SELECT：

SELECT * FROM x WHERE a = 1 AND b = 2 AND c = 3
=> If nothing found, try: SELECT * FROM x WHERE a = 1 AND b = 2 AND c = 0
=> If nothing found, try: SELECT * FROM x WHERE a = 1 AND b = 0 AND c = 0

其中至少有一个有结果，但所有情况都可能有结果。我想合并这个逻辑并仅返回一个案例，即具有最多给定（！= 0）条件的案例。

谢谢！

Answer 1

我可以使用UNION查询回答并且不是EXISTS：

SELECT * FROM x
WHERE
  (a, b, c) = (
      SELECT a, b, c
      FROM x WHERE (a, b, c) IN ( (1,2,3), (1,2,0), (1,0,0) )
      ORDER BY (b=0) + (c=0)
      LIMIT 1
  )

但更聪明的解决方案是这样的：

{{1}}

我不确定这最后一个会有更好的表现。我会尝试哪一个更好。

合并多个级联选择，优先级

1 个答案: