Sql server 2012 SQL查询优化2012

我有一个名为

SnackMaster

的表。其结构如下：

SnackID        int
SnackName      varchar(100)
SnackAmount    decimal(18,2)

e、 g:

还有另一个名为

SnacksOrderDetais

的表，其中包含来自员工的零食订单。其结构如下所示：

OrderID        int
EmployeeID     int  
SnackCount     tinyint
TotalAmount    decimal(18,2)
orderDate      date

e、 g:

我需要一份小吃摘要，如下所示：

SnacksName   : Tea,
SnackCount   : 4 (that is 2 each from the above two orders),
TotalAmount  : 40 (twenty from each orders)

我使用以下查询来获得结果。结果是确定的，但我想知道是否有任何其他优化查询可用

SELECT DISTINCT SOD.SnacksID
    ,SnacksName
    ,(SELECT SUM(SnacksCount) 
      FROM SnacksOrderDetails 
      WHERE SnacksID = SOD.SnacksID ) AS SnacksCount
FROM SnacksOrderDetails SOD
INNER JOIN SnacksMaster SM ON SOD.SnacksID = SM.SnacksID
WHERE SOD.OrderedOn = @OrderDate 

---

使用GROUP BY获得相同的结果。大概是这样的：

SELECT SOD.SnacksID, SnacksName, SUM(SnacksCount) AS SnacksCount 
FROM SnacksOrderDetails SOD 
INNER JOIN SnacksMaster SM ON SOD.SnacksID = SM.SnacksID 
WHERE SOD.OrderedOn = @OrderDate
GROUP BY SOD.SnacksID

---

请澄清TotalAmount和SnackCount之间的区别

从这里开始：

SELECT SM.SnacksName,
        SUM(SOD.SnacksCount) AS SnacksCount
FROM SnacksMaster SM 
INNER JOIN SnacksOrderDetails SOD ON SOD.SnacksID = SM.SnacksID AND SOD.OrderedOn = @OrderDate
GROUP BY SM.SnacksName

---

是的，没错。不知何故，他忽略了这一点。现在更正。

SELECT SOD.SnacksID, SnacksName, SUM(SnacksCount) AS SnacksCount 
FROM SnacksOrderDetails SOD 
INNER JOIN SnacksMaster SM ON SOD.SnacksID = SM.SnacksID 
WHERE SOD.OrderedOn = @OrderDate
GROUP BY SOD.SnacksID

SELECT SM.SnacksName,
        SUM(SOD.SnacksCount) AS SnacksCount
FROM SnacksMaster SM 
INNER JOIN SnacksOrderDetails SOD ON SOD.SnacksID = SM.SnacksID AND SOD.OrderedOn = @OrderDate
GROUP BY SM.SnacksName