SQL

Question

我查询 return 的客户回复。响应 table (rp) 加入到客户 table (ah)。查询return是我想要的结果。

但是，如果记录了多个有效响应，则每个客户 return 的响应超过 1 个。

所以我试图通过添加一个 HAVING 子句来限制它，但我无法与 responsefreetxt 分组，因为它是 NTEXT。

SELECT 
    ah.CUSTACCOUNT,         /--- type = CHAR
    rp.RESPONSEFREETXT      /--- type = NTEXT
FROM 
    ah
INNER JOIN 
    rp ON rp.CUSTACCOUNT = ah.CUSTACCOUNT
    ...
WHERE 
    ah.ACTIVE = 1
    AND rp.ACTIVE = 1
    AND ...
GROUP BY 
    ah.CUSTACCOUNT, rp.RESPONSEFREETXT
HAVING 
    COUNT(ah.CUSTACCOUNT) = 1
ORDER BY 
    rp.date DESC

导致此错误：

Msg 306, Level 16, State 2, Line 21
The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.

理想情况下，我希望每个客户 return 1 行，在重复的情况下，只有 return 最近的响应。

我该怎么做？

谢谢！

Answer 1

从 SQL 服务器处理此问题的一种方法是使用 ROW_NUMBER:

WITH cte AS (
    SELECT ah.CUSTACCOUNT, rp.RESPONSEFREETXT,
           ROW_NUMBER() OVER (PARTITION BY ah.CUSTACCOUNT
                              ORDER BY rp.SOME_DATE DESC) rn
    FROM ah
    INNER JOIN rp ON rp.CUSTACCOUNT = ah.CUSTACCOUNT
    ...    
    WHERE ah.ACTIVE = 1 AND rp.ACTIVE = 1 AND ...
    -- I have removed the GROUP BY clause
)

SELECT *
FROM cte
WHERE rn = 1;

这假设在响应 table 中存在一个名为 SOME_DATE 的列，它跟踪每个客户响应的时间戳。编写上述查询的另一种方法是使用 TOP 1 WITH TIES:

SELECT TOP 1 WITH TIES ah.CUSTACCOUNT, rp.RESPONSEFREETXT
FROM ah
INNER JOIN rp ON rp.CUSTACCOUNT = ah.CUSTACCOUNT
...    
WHERE ah.ACTIVE = 1 AND rp.ACTIVE = 1 AND ...
ORDER BY ROW_NUMBER() OVER (PARTITION BY ah.CUSTACCOUNT
                            ORDER BY rp.SOME_DATE DESC);

SQL - 删除重复项，使用 HAVING 子句和 NTEXT 列选择最近的

SQL - Removing duplicates, selecting most recent using HAVING clause & an NTEXT column

sql-server

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having