如何修复“文本、ntext 和图像数据类型无法比较或排序，除非使用 IS NULL 或 LIKE 运算符。”

Question

这是我到目前为止：

SELECT 
    account, ' ', message_type, 
    MAX(message_no) as max_message_no, message_text
FROM
    (SELECT 
         account, message_type, message_no, message_text
     FROM  
         messages m 
     INNER JOIN 
         receivables r ON m.account = r.aracct
     WHERE 
         m.account IN (SELECT r.aracct AS account 
                       FROM receivables r 
                       WHERE r.balance <> 0)
         AND m.message_type = 'N') t1
GROUP BY 
    t1.account, t1.message_type, t1.message_text

我不断收到错误消息：

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。

我基本上想要message_no每个帐户的最大值，我希望它显示message_text，但它不允许它，因为它是一种text数据类型。

Answer 1

TEXT,NTEXT和IMAGE已弃用，应替换为相应的类型VARCHAR(MAX),NVARCHAR(MAX)和VARBINARY(MAX)。你可能会用你的TEXT-column

CAST(t1.message_text AS VARCHAR(MAX))

在您的子选择中执行一次可能就足够了：

SELECT account, ' ', message_type, MAX(message_no) as max_message_no, message_text
FROM
(
SELECT account, message_type, message_no, CAST(message_text AS VARCHAR(MAX)) AS message_text
    FROM messages m INNER JOIN receivables r ON m.account = r.aracct
        WHERE m.account IN (SELECT r.aracct AS account FROM receivables r WHERE r.balance <> 0)
        AND m.message_type = 'N'
) t1
GROUP BY t1.account, t1.message_type, t1.message_text