SET @dtEndDate = DATEADD(DD, -1, CAST(CAST((MONTH(@dtEndDate) + 1) AS
VARCHAR(2)) + '/01/' + CAST(YEAR(@dtEndDate) AS VARCHAR(4)) + ' 23:59:59' AS DATETIME))
SET @dtStartDate = DATEADD(MM, -1 * 12, @dtEndDate)
-- Get all months into the first table
SET @i = 0
WHILE (@i < 12)
BEGIN
SET @dtDate = DATEADD(mm, -1 * @i, @dtEndDate)
INSERT INTO @tblMonths SELECT CAST(YEAR(@dtDate) AS VARCHAR(4)) + '-' +
CASE
WHEN MONTH(@dtDate) < 10
THEN '0' + CAST(MONTH(@dtDate) AS VARCHAR(2))
ELSE CAST(MONTH(@dtDate) AS VARCHAR(2))
END AS sMonth
SET @i = @i + 1
END
-- Get all clients who had sales during that period into the "y" table
INSERT INTO @tblCustomers
SELECT DISTINCT
c.CustomerID,
c.CompanyName,
c.ContactName
FROM Customers c
INNER JOIN Orders o ON c.CustomerID = o.CustomerID
WHERE o.OrderDate BETWEEN @dtStartDate AND @dtEndDate
INSERT INTO @tblFinal
SELECT m.sMonth,
c.CustomerID,
c.CompanyName,
c.ContactName,
0
FROM @tblMonths m CROSS JOIN @tblCustomers c
UPDATE @tblFinal SET
mSales = mydata.mSales
FROM @tblFinal f INNER JOIN
(
SELECT c.CustomerID,
CAST(YEAR(o.OrderDate) AS VARCHAR(4)) + '-' +
CASE WHEN MONTH(o.OrderDate) < 10
THEN '0' + CAST(MONTH(o.OrderDate) AS VARCHAR(2))
ELSE CAST(MONTH(o.OrderDate) AS VARCHAR(2))
END AS sMonth,
SUM(od.Quantity * od.UnitPrice) AS mSales
FROM Customers c
INNER JOIN Orders o ON c.CustomerID = o.CustomerID
INNER JOIN [Order Details] od ON o.OrderID = od.OrderID
WHERE o.OrderDate BETWEEN @dtStartDate AND @dtEndDate
GROUP BY
c.CustomerID,
CAST(YEAR(o.OrderDate) AS VARCHAR(4)) + '-' +
CASE WHEN MONTH(o.OrderDate) < 10
THEN '0' + CAST(MONTH(o.OrderDate) AS VARCHAR(2))
ELSE CAST(MONTH(o.OrderDate) AS VARCHAR(2))
END
) mydata on f.CustomerID = mydata.CustomerID AND f.sMonth =
mydata.sMonth
SELECT f.sMonth,
f.CustomerID,
f.CompanyName,
f.ContactName,
f.mSales
FROM @tblFinal f
ORDER BY
f.CompanyName,
f.sMonth
5, 拾遗补零
这里介绍其他一些可帮助提高 SQL 查询效率的常用技术。假设您将按区域对所有销售人员进行分组并将他们的销售额进行小计，但是您只想要那些数据库中标记为处于活动状态的销售人员。您可以按区域对销售人员分组，并使用 HAVING 子句消除那些未处于活动状态的销售人员，也可以在 WHERE 子句中执行此操作。在 WHERE 子句中执行此操作会减少需要分组的行数，所以比在 HAVING 子句中执行此操作效率更高。HAVING 子句中基于行的条件的筛选会强制查询对那些在 WHERE 子句中会被去除的数据进行分组。