Question

有没有办法让以下工作？

SELECT
(SELECT COUNT(foo) FROM table2 WHERE table1.id = table2.id) AS foos
CASE
WHEN foos <= 0 THEN 0
WHEN foos > 0 THEN 1
END
AS isFoos
FROM table1

我得到它的唯一方法是：

SELECT
(SELECT COUNT(foo) FROM table2 WHERE table1.id = table2.id) AS foos
CASE
WHEN (SELECT COUNT(foo) FROM table2 WHERE table1.id = table2.id) <= 0 THEN 0
WHEN (SELECT COUNT(foo) FROM table2 WHERE table1.id = table2.id) > 0 THEN 1
END
AS isFoos
FROM table1

它看起来非常可怕。

请注意，该示例并未描述我有问题的SQL查询，它描述了我想要从查询中获取的语法。

谢谢：）

编辑：修正了SQL以更好地解释问题。

编辑2：这是小提琴，我希望它有所帮助。

http://sqlfiddle.com/#!2/18a45d/2

小提琴包含产品和产品线。产品可以多条生产线，生产线可以生产多种产品。

pr_connected显示应该使用该产品的行数，SELECT计数显示实际使用该产品的行数。

我使用的数据库有一些缺陷，由于写入的代码量不能修复它们。

Answer 1

SELECT IF(COUNT('foo') > 0, 1, 0) as `isFoos` FROM `table1`

OR

SELECT
  `t`.`foos`,
  IF(`t`.`foos` > 0, 1, 0) as `isFoos`
FROM
  (SELECT COUNT(`x`) AS `foos` FROM `stackoverflow`) as `t`

Answer 2

我将根据您的更新和sqlfiddle使用新查询。我将使用子查询，但只有一个COUNT(*)聚合函数，它将与您的结果相同。

SELECT pr_id, pr_name, connected, 
 CASE
  WHEN connected <= 0 THEN "RED"
  WHEN connected < pr_connected THEN "YELLOW"
  WHEN connected >= pr_connected THEN "GREEN"
 END as Status
FROM (
   SELECT pr_id, pr_name, pr_connected, 
     ( SELECT COUNT(pl_id) FROM product_line WHERE pl_product_id = pr_id) AS connected
       FROM product
       GROUP BY pr_name 
      ) tt

检查我的 Fiddle Demo

Answer 3

希望这会有所帮助：

select email,
case 
when count(email) > 2 then 55
when count(email) < 2 then 33
end 
as cc
from supportContacts
group by email

我在这里提出了一个SQL小提琴http://sqlfiddle.com/#!2/94e3dd/10

使用从CASE中的另一个SELECT获取的字段

3 个答案: