MySQL UNION - 检测几个 SELECT 的返回结果

Question

我有两个 SELECT 查询与 UNION 合并。这是 MySQL 查询:

SELECT `id`,`type`,`text`
  FROM my_table 
 WHERE position = '1' 
   AND status = '1' 
   AND targeting = 'all'
UNION
SELECT `id`,`type`,`text` 
  FROM my_table 
 WHERE position = '1' 
   AND status = '1' 
   AND targeting LIKE '%US%'

我如何才能找出这两个 SELECT 查询中的哪一个以 TRUE 执行以便从所需的行中获取结果？

Answer 1

您可以向查询添加一个额外的列，该列根据查询的哪一部分成功返回不同的常量:

SELECT 'query1' AS `src`, `id`, `type`, `text`
FROM my_table
WHERE position = '1' AND status = '1' AND targeting = 'all'

UNION ALL

SELECT 'query2' AS `src`, `id`, `type`, `text`
FROM my_table
WHERE position = '1' AND status = '1' AND targeting LIKE '%US%'

同样在这种情况下，您根本不需要 UNION:

SELECT
    targeting LIKE '%US%' AS `targeting_like_us`,
    targeting = 'all' AS `targeting_equals_all`,
    `id`,
    `type`,
    `text`
FROM my_table
WHERE position = '1'
AND status = '1'
AND (targeting LIKE '%US%' OR targeting = 'all')