四项技术提高SQL Server的性能

您已经看到了，有大量技术都可用于优化查询和实现特定的业务规则，技巧就是进行一些尝试，然后比较它们的性能。最重要的是要测试、测试、再测试。
　　Figure 2 Returning All Customers and Their Sales
　　set nocount on
　　DECLARE @dtStartDate DATETIME,
　　@dtEndDate DATETIME,
　　@dtDate DATETIME
　　SET @dtEndDate = '5/5/1997'
　　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)
　　SELECT 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,
　　c.CustomerID,
　　c.CompanyName,
　　c.ContactName,
　　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
　　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,
　　c.CustomerID,
　　c.CompanyName,
　　c.ContactName
　　ORDER BY
　　c.CompanyName,
　　sMonth
　　Figure 3 Cartesian Product at Work
　　DECLARE @tblMonths TABLE (sMonth VARCHAR(7))
　　DECLARE @tblCustomers TABLE ( CustomerID CHAR(10),
　　CompanyName VARCHAR(50),
　　ContactName VARCHAR(50))
　　DECLARE @tblFinal TABLE ( sMonth VARCHAR(7),
　　CustomerID CHAR(10),
　　CompanyName VARCHAR(50),
　　ContactName VARCHAR(50),
　　mSales MONEY)
　　DECLARE @dtStartDate DATETIME,
　　@dtEndDate DATETIME,
　　@dtDate DATETIME,
　　@i INTEGER
　　SET @dtEndDate = '5/5/1997'
　　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