SQL嵌套查询，最大值，分组

我的表（名为Inventory）如下所示：

SELECT InventoryType, LocationID, InventoryLevel,
       SafetyStock, MaxLevel, ModifiedAt
FROM Inventory
WHERE LocationID = 2 AND ModifiedAt IN
     (SELECT TOP 1 ModifiedAt 
      FROM Inventory
      WHERE LocationID = 2
      ORDER BY ModifiedAt DESC);

InventoryType、LocationID、InventoryLevel、SafetyStock、MaxLevel、ModifiedAt

擦除器，1,14,3,15,11-2014

擦除器，2,4,10,50,10-2014

擦除器，2,5,10,50,11-2014

铅笔，1,10,5,45,11-2014

铅笔，2,23,15,50,11-2014

Pens，1,9,10,50,11-2014

Pens，2,55,10,50,12-2014

有三个主键：InventoryType、LocationID和ModifiedAt

给定指定的LocationID，我希望查询返回每个不同InventoryType的all，其中返回的每个元组的日期是具有指定LocationID的给定库存类型的记录中最近的ModifiedAt日期。例如，LocationID=2将返回：

InventoryType、LocationID、InventoryLevel、SafetyStock、MaxLevel、ModifiedAt

擦除器，2,5,10,50,11-2014

铅笔，2,23,15,50,11-2014

Pens，2,55,10,50,12-2014

我迄今为止的努力如下：

SELECT InventoryType, LocationID, InventoryLevel,
       SafetyStock, MaxLevel, ModifiedAt
FROM Inventory
WHERE LocationID = 2 AND ModifiedAt IN
     (SELECT TOP 1 ModifiedAt 
      FROM Inventory
      WHERE LocationID = 2
      ORDER BY ModifiedAt DESC);

我的查询返回：

InventoryType,LocationID,InventoryLevel,SafetyStock,MaxLevel,ModifiedAt
Pens,2,55,10,50,12-2014

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任何帮助都将不胜感激。

您需要一个相关的子查询。请尝试以下方法：

SELECT InventoryType, LocationID, InventoryLevel, SafetyStock, MaxLevel, ModifiedAt
FROM Inventory as i
WHERE LocationID = 2 AND
      ModifiedAt IN (SELECT TOP 1 i2.ModifiedAt
                     FROM Inventory as i2
                     WHERE i2.LocationID = 2 AND i2.InventoryType = i.InventoryType
                     ORDER BY i2.ModifiedAt DESC
                    );

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使用

SELECT DISTINCT

选择DISTINCT

InventoryType

SELECT DISTINCT InventoryType, LocationID, 
InventoryLevel, SafetyStock, MaxLevel, ModifiedAt
FROM Inventory
WHERE LocationID = 2
AND ModifiedAt IN 
(SELECT TOP 1 ModifiedAt FROM Inventory WHERE LocationID = 2 ORDER BY ModifiedAt DESC)

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我糟糕的，出于某种原因被转录成MonthYear。无论如何，这似乎正是我所需要的。非常感谢。