SQL Server子查询返回了多个值。 当子查询跟随（字符）或子查询用作表达式时，不允许这样做

Question

我试图根据它们的出现更新一些字段。 如果它们只出现一次，我正在更新一些状态字段。

我目前的代码如下：

UPDATE table1
SET statusField = 1
WHERE someID = (
               SELECT someID
               FROM table1
               GROUP BY someID HAVING COUNT(*) = 1
               )

这将返回一个错误，如标题中的错误： Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

还有其他易于阅读/简单的解决方案吗？

Answer 1

使用IN关键字而不是equals运算符，如下所示：

UPDATE table1
SET statusField = 1
WHERE someID IN (
           SELECT someID
           FROM table1
           GROUP BY someID HAVING COUNT(*) = 1
           )

使用=要求子查询返回1个结果。 IN关键字适用于列表。

Answer 2

您应该在子选择中加入表格。 可以使用'in'，但在你的情况下我会使用exists：

UPDATE table1 x
SET statusField = 1
WHERE exists (
               SELECT null
               FROM table1
               WHERE x.someID = someID
               GROUP BY someID 
               HAVING COUNT(*) = 1
               )

为了获得更好的性能，我会使用这个脚本（sqlserver-2008 +）：

;WITH x as
(
SELECT rc = count() over (partition by someID), statusField
FROM table1
)
UPDATE x
SET statusField = 1
WHERE rc = 1

Answer 3

尝试这个

使用Top

UPDATE table1
SET statusField = 1
WHERE someID = (
               SELECT TOP 1 someID
               FROM table1
               GROUP BY someID HAVING COUNT(*) = 1
               )

或者你可以使用IN子句

UPDATE table1
SET statusField = 1
WHERE someID IN (
               SELECT someID
               FROM table1
               GROUP BY someID HAVING COUNT(*) = 1
               )