SQL Server的最大日期子查询

我试图在子查询中加入最大日期，但出现错误。我正在使用SQL server

SELECT Headcount.[Snapshot Date]
, Headcount.[ID]
, Assessment.[Assessment Date]
, Assessment.[Code]

FROM Headcount INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] = 
                 (SELECT MAX(CAST(Assessment.[Assessment Date] as datetime)) 
                  FROM Assessmnet AS Z 
                  WHERE Z.[ID] = Assessment.[ID] 
                       AND Assessment.[Assessment Date] <= Headcount.[Snapshot Date]
                 )

但我有一个错误：

聚合不能出现在WHERE子句中，除非它位于HAVING子句或select列表中包含的子查询中，并且被聚合的列是外部引用

---

您忘记了在子查询中指定的别名Z。如果在子查询中使用评估，则他会考虑来自外部查询的评估，因为评估在子查询中的名称为Z

SELECT Headcount.[Snapshot Date]
, Headcount.[ID]
, Assessment.[Assessment Date]
, Assessment.[Code]

FROM Headcount INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] = 
                 (SELECT MAX(CAST(Z.[Assessment Date] as datetime)) 
                  FROM Assessment AS Z 
                  WHERE Z.[ID] = Assessment.[ID] 
                       AND Z.[Assessment Date] <= Headcount.[Snapshot Date]
                 )

---

您忘记了在子查询中指定的别名Z。如果在子查询中使用评估，则他会考虑来自外部查询的评估，因为评估在子查询中的名称为Z

SELECT Headcount.[Snapshot Date]
, Headcount.[ID]
, Assessment.[Assessment Date]
, Assessment.[Code]

FROM Headcount INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] = 
                 (SELECT MAX(CAST(Z.[Assessment Date] as datetime)) 
                  FROM Assessment AS Z 
                  WHERE Z.[ID] = Assessment.[ID] 
                       AND Z.[Assessment Date] <= Headcount.[Snapshot Date]
                 )

---

问题在where条件的子查询中，请尝试以下操作：

SELECT
    Headcount.[Snapshot Date],
    Headcount.[ID],
    Assessment.[Assessment Date],
    Assessment.[Code]
FROM Headcount
INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] =
(
    SELECT
        MAX(CAST(Assessment.[Assessment Date] AS DATETIME))
    FROM Assessmnet AS Z
    GROUP BY
        Z.ID
    HAVING Z.[ID] = Assessment.[ID]
           AND Assessment.[Assessment Date] <= Headcount.[Snapshot Date]
);

---

问题在where条件的子查询中，请尝试以下操作：

SELECT
    Headcount.[Snapshot Date],
    Headcount.[ID],
    Assessment.[Assessment Date],
    Assessment.[Code]
FROM Headcount
INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] =
(
    SELECT
        MAX(CAST(Assessment.[Assessment Date] AS DATETIME))
    FROM Assessmnet AS Z
    GROUP BY
        Z.ID
    HAVING Z.[ID] = Assessment.[ID]
           AND Assessment.[Assessment Date] <= Headcount.[Snapshot Date]
);

您应该将MAXCASTZ.[Assessment Date]写为datetime，而不是将MAXCASTAssessment.[Assessment Date]写为datetime。否则，您将聚合到错误的表中

以下查询可能未经测试即可工作！：

SELECT Headcount.[Snapshot Date]
, Headcount.[ID]
, Assessment.[Assessment Date]
, Assessment.[Code]
FROM Headcount
INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] =
                 (SELECT MAX(CAST(Z.[Assessment Date] as datetime))
                  FROM Assessment AS Z
                  WHERE Z.[ID] = Assessment.[ID] 
                    AND Z.[Assessment Date] <= Headcount.[Snapshot Date])

您还可以重写它，以用于为每个评估选择最近的行：

SELECT [Snapshot Date], [ID], [Assessment Date], [Code]
FROM (SELECT [Snapshot Date], [ID], [Assessment Date], [Code],
        ROW_NUMBER() OVER (PARTITION BY [ID] ORDER BY [Assessment Date] DESC) rn
      FROM Headcount JOIN Assessment USING ([ID])
      WHERE [Assessment Date] <= [Snapshot Date]) t
WHERE rn = 1

您应该将MAXCASTZ.[Assessment Date]写为datetime，而不是将MAXCASTAssessment.[Assessment Date]写为datetime。否则，您将聚合到错误的表中

以下查询可能未经测试即可工作！：

SELECT Headcount.[Snapshot Date]
, Headcount.[ID]
, Assessment.[Assessment Date]
, Assessment.[Code]
FROM Headcount
INNER JOIN Assessment ON Assessment.[ID] = Headcount.[ID]
WHERE Assessment.[Assessment Date] =
                 (SELECT MAX(CAST(Z.[Assessment Date] as datetime))
                  FROM Assessment AS Z
                  WHERE Z.[ID] = Assessment.[ID] 
                    AND Z.[Assessment Date] <= Headcount.[Snapshot Date])

您还可以重写它，以用于为每个评估选择最近的行：

SELECT [Snapshot Date], [ID], [Assessment Date], [Code]
FROM (SELECT [Snapshot Date], [ID], [Assessment Date], [Code],
        ROW_NUMBER() OVER (PARTITION BY [ID] ORDER BY [Assessment Date] DESC) rn
      FROM Headcount JOIN Assessment USING ([ID])
      WHERE [Assessment Date] <= [Snapshot Date]) t
WHERE rn = 1