除非使用IS NULL或LIKE>运算符,否则无法比较或排序text,ntext和image data>类型

Question

电子邮件属于表格预订,在Microsoft sql server中定义为"文本"类型

SELECT email, 
 COUNT(email) AS NumOccurrences
FROM Booking
GROUP BY email
HAVING ( COUNT(email) > 1 )

运行上述查询后(尝试在预订中查找重复的电子邮件),我收到如下错误消息:

除非使用IS NULL或LIKE运算符,否则无法比较或排序text,ntext和image数据类型.

我正在使用Microsoft Sql

Answer 1

既然您正在使用SQL Server,为什么不将数据类型更改为VARCHAR(100)？

要在不更改数据类型的情况下解决此错误,TEXT or NTEXT需要将该列转换为VARCHAR or NVARCHAR在语句的ORDER BY子句或GROUP BY子句中使用时SELECT.例如,这有点混乱

SELECT  CAST(email AS NVARCHAR(100)) email, 
        COUNT(CAST(email AS NVARCHAR(100))) AS NumOccurrences
FROM    Booking
GROUP   BY CAST(email AS NVARCHAR(100))
HAVING  COUNT(CAST(email AS NVARCHAR(100))) > 1 

• SQL Server错误消息 - 消息306