仅使用最新日期 SQL 更新 ID(6 个中的 2 个)

Updating only ID#39;s with the latest date SQL (2 of 6)(仅使用最新日期 SQL 更新 ID(6 个中的 2 个))

问题描述

我有以下表格:

和:

我制定了这个查询:

Update Table 1 
SET DY_H_ID = ( 

    SELECT MAX(ID) 
    FROM Table 2
    WHERE H_DateTime <= DY_Date 
    AND H_IDX = DY_IDX 
    AND H_HA_ID = 7 
    AND H_HSA_ID = 19 
    AND H_Description LIKE 'Diary item added for :%'

) 
WHERE DY_H_ID IS NULL AND DY_IDX IS NOT NULL

结果如下:

但是，此查询会更新所有 6 行.我只需要用最新日期更新两行，即 '2013-08-29 15:00:00.000'.这意味着 6 条记录中只有 2 条会被更新，另外 4 条将保持为 NULL.

However, this query updates all 6 rows. I need to update only the two rows with the latest date, that would be '2013-08-29 15:00:00.000'. That would mean only 2 of the 6 records would be updated and the other 4 would remain NULL.

如何通过添加到上述查询来做到这一点?我知道这可能并不理想，但别无选择，只能做这样的事情.我不明白的是你如何只选择最新的日期而不对其进行硬编码.此数据可能会发生变化，并且不会总是相同的日期等.

How can I do this by adding to the above query? I know this might not be ideal but there is no option but to do something like this. What I don't understand is how do you select only the latest dates without hardcoding it. This data can change and it won't always be the same dates etc.

推荐答案

试试这个:

UPDATE TABLE 1 
SET    DY_H_ID = (SELECT Max(ID) 
                  FROM   TABLE 2 
                  WHERE  H_DATETIME <= DY_DATE 
                         AND H_IDX = DY_IDX 
                         AND H_HA_ID = 7 
                         AND H_HSA_ID = 19 
                         AND H_DESCRIPTION LIKE 'Diary item added for :%') 
WHERE  DY_H_ID IS NULL 
       AND DY_IDX IS NOT NULL 
       AND DY_DATE = (SELECT Max(DY_DATE) 
                      FROM   TABLE1) 

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