sql - SQL 子查询 COUNT CASE

Question

如果嵌套子查询的计数为 0，我希望 SELECT 查询返回特定值...

SELECT
  ( SELECT (CASE COUNT(*) = 0 THEN 'TRUE' ELSE 'FALSE' END)
    FROM List
    WHERE Status = 1
      AND Deleted = 1
  ) AS Status

这不起作用这种语法有什么问题？

Answer 1

我相信你想要一个看起来像这样的案例陈述：

CASE
 WHEN EXISTS(SELECT * FROM list WHERE Status = 1 AND Deleted = 1) THEN 'FALSE'
 ELSE 'TRUE'
END

Answer 2

您的查询缺少 CASE 语句中的 WHEN 关键字。

SELECT
  ( SELECT (CASE WHEN COUNT(*) = 0 THEN 'TRUE' ELSE 'FALSE' END)
    FROM List
    WHERE Status = 1
      AND Deleted = 1
  ) AS Status

您可以使用它，也可以通过删除外部 SELECT 语句来简化查询。而且，括号也是可选的。

SELECT CASE WHEN COUNT(*) = 0 THEN 'TRUE' ELSE 'FALSE' END
FROM List
WHERE Status = 1
  AND Deleted = 1