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
               )

这会返回一个错误,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.

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关键字在列表中有效.