SQL 服务器：Select WHERE 字段不能包含 VALUE

Question

我知道标题含糊不清，但我不确定如何措辞。

我有一个简单的table（见下图）。

我需要编写一个 SQL 语句来检索代表每个 [UNIT_ID] 和 [ISACTIVE] 的单个记录，其中 [ISACTIVE] 是该特定 [=13] 的最大值=].

理想情况下，结果应如下所示（注意 UNIT_ID=2 没有 ISACTIVE=1）：

做一个简单的 [ISACTIVE] > 0 是不是我要找的东西，因为那样 UNIT_ID=2 永远不会出现在记录中。

这是我尝试过的（失败）：

SELECT 
    [ID], [UNIT_ID], [REV], [ISACTIVE], [DATE_ENTERED] 
FROM 
    TestTable 
WHERE
    ([ISACTIVE] = (SELECT MAX([ISACTIVE]) 
                   FROM TestTable 
                   WHERE ([UNIT_ID] = [UNIT_ID])));

-- This code only reveals two records (its missing record #4)

如有任何帮助，我们将不胜感激！

Answer 1

与NOT EXISTS:

SELECT t.[ID], t.[UNIT_ID], t.[REV], t.[ISACTIVE], t.[DATE_ENTERED] 
FROM TestTable AS t
WHERE NOT EXISTS (
  SELECT 1 FROM TestTable
  WHERE [UNIT_ID] = t.[UNIT_ID] AND [ISACTIVE] > t.[ISACTIVE]
)

或 ROW_NUMBER():

SELECT t.[ID], t.[UNIT_ID], t.[REV], t.[ISACTIVE], t.[DATE_ENTERED] 
FROM (
  SELECT *, 
    ROW_NUMBER() OVER (PARTITION BY [UNIT_ID] ORDER BY [ISACTIVE] DESC) AS rn
  FROM TestTable
) AS t
WHERE t.rn = 1

Answer 2

您的代码的问题是子查询没有为 TestTable 使用别名。应该是

SELECT 
   [ID], [UNIT_ID], [REV], [ISACTIVE], [DATE_ENTERED] 
FROM TestTable ta
WHERE (
    [ISACTIVE]=
        (SELECT MAX(t.[ISACTIVE]) FROM TestTable t WHERE (t.[UNIT_ID]=ta.[UNIT_ID])));

Answer 3

正如@forpas 所说，我认为最好的选择是：

SELECT t.[ID], t.[UNIT_ID], t.[REV], t.[ISACTIVE], t.[DATE_ENTERED] 
FROM (
  SELECT *, 
    ROW_NUMBER() OVER (PARTITION BY [UNIT_ID] ORDER BY [UNIT_ID, ISACTIVE] DESC) AS row_number
  FROM TestTable
) AS t
WHERE t.row_number = 1

唯一的区别是 order by 子句，它必须包含那些列 UNIT_ID, ISACTIVE.

希望对您有所帮助。

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