Microsoft SQL Server 2008技术内幕:T-SQL查询---------查询优化

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原文链接：http://www.cnblogs.com/Gravin-Gu/archive/2013/01/30/2883710.html

文章标签：

#数据库 #runtime

本文详细介绍了一个SQL性能优化的实战案例，包括快速建立数值表、生成随机数据、优化方法论、系统等待信息分析、数据库IO分析、跟踪工作负载、查询计划统计及查询IO和运行时间的测量。

示例数据库:

-- Sample Data for this Chapter

-- Listing 4-1: Creation Script for Sample Database and Tables
SET NOCOUNT ON;
USE master;
IF DB_ID('Performance') IS NULL
  CREATE DATABASE Performance;
GO
USE Performance;
GO

-- Creating and Populating the Nums Auxiliary Table
SET NOCOUNT ON;
IF OBJECT_ID('dbo.Nums', 'U') IS NOT NULL
  DROP TABLE dbo.Nums;
CREATE TABLE dbo.Nums(n INT NOT NULL PRIMARY KEY);

DECLARE @max AS INT, @rc AS INT;
SET @max = 1000000;
SET @rc = 1;

INSERT INTO dbo.Nums(n) VALUES(1);
WHILE @rc * 2 <= @max
BEGIN
  INSERT INTO dbo.Nums(n) SELECT n + @rc FROM dbo.Nums;
  SET @rc = @rc * 2;
END

INSERT INTO dbo.Nums(n)
  SELECT n + @rc FROM dbo.Nums WHERE n + @rc <= @max;
GO

-- Drop Data Tables if Exist
IF OBJECT_ID('dbo.EmpOrders', 'V') IS NOT NULL
  DROP VIEW dbo.EmpOrders;
GO
IF OBJECT_ID('dbo.Orders', 'U') IS NOT NULL
  DROP TABLE dbo.Orders;
GO
IF OBJECT_ID('dbo.Customers', 'U') IS NOT NULL
  DROP TABLE dbo.Customers;
GO
IF OBJECT_ID('dbo.Employees', 'U') IS NOT NULL
  DROP TABLE dbo.Employees;
GO
IF OBJECT_ID('dbo.Shippers', 'U') IS NOT NULL
  DROP TABLE dbo.Shippers;
GO

-- Data Distribution Settings
DECLARE
  @numorders   AS INT,
  @numcusts    AS INT,
  @numemps     AS INT,
  @numshippers AS INT,
  @numyears    AS INT,
  @startdate   AS DATETIME;

SELECT
  @numorders   =   1000000,
  @numcusts    =     20000,
  @numemps     =       500,
  @numshippers =         5,
  @numyears    =         4,
  @startdate   = '20050101';

-- Creating and Populating the Customers Table
CREATE TABLE dbo.Customers
(
  custid   CHAR(11)     NOT NULL,
  custname NVARCHAR(50) NOT NULL
);

INSERT INTO dbo.Customers(custid, custname)
  SELECT
    'C' + RIGHT('000000000' + CAST(n AS VARCHAR(10)), 10) AS custid,
    N'Cust_' + CAST(n AS VARCHAR(10)) AS custname
  FROM dbo.Nums
  WHERE n <= @numcusts;

ALTER TABLE dbo.Customers ADD
  CONSTRAINT PK_Customers PRIMARY KEY(custid);

-- Creating and Populating the Employees Table
CREATE TABLE dbo.Employees
(
  empid     INT          NOT NULL,
  firstname NVARCHAR(25) NOT NULL,
  lastname  NVARCHAR(25) NOT NULL
);

INSERT INTO dbo.Employees(empid, firstname, lastname)
  SELECT n AS empid,
    N'Fname_' + CAST(n AS NVARCHAR(10)) AS firstname,
    N'Lname_' + CAST(n AS NVARCHAR(10)) AS lastname
  FROM dbo.Nums
  WHERE n <= @numemps;

ALTER TABLE dbo.Employees ADD
  CONSTRAINT PK_Employees PRIMARY KEY(empid);

-- Creating and Populating the Shippers Table
CREATE TABLE dbo.Shippers
(
  shipperid   VARCHAR(5)   NOT NULL,
  shippername NVARCHAR(50) NOT NULL
);

INSERT INTO dbo.Shippers(shipperid, shippername)
  SELECT shipperid, N'Shipper_' + shipperid AS shippername
  FROM (SELECT CHAR(ASCII('A') - 2 + 2 * n) AS shipperid
        FROM dbo.Nums
        WHERE n <= @numshippers) AS D;

ALTER TABLE dbo.Shippers ADD
  CONSTRAINT PK_Shippers PRIMARY KEY(shipperid);

-- Creating and Populating the Orders Table
CREATE TABLE dbo.Orders
(
  orderid   INT        NOT NULL,
  custid    CHAR(11)   NOT NULL,
  empid     INT        NOT NULL,
  shipperid VARCHAR(5) NOT NULL,
  orderdate DATETIME   NOT NULL,
  filler    CHAR(155)  NOT NULL DEFAULT('a')
);

INSERT INTO dbo.Orders(orderid, custid, empid, shipperid, orderdate)
  SELECT n AS orderid,
    'C' + RIGHT('000000000'
            + CAST(
                1 + ABS(CHECKSUM(NEWID())) % @numcusts
                AS VARCHAR(10)), 10) AS custid,
    1 + ABS(CHECKSUM(NEWID())) % @numemps AS empid,
    CHAR(ASCII('A') - 2
           + 2 * (1 + ABS(CHECKSUM(NEWID())) % @numshippers)) AS shipperid,
      DATEADD(day, n / (@numorders / (@numyears * 365.25)), @startdate)
        -- late arrival with earlier date
        - CASE WHEN n % 10 = 0
            THEN 1 + ABS(CHECKSUM(NEWID())) % 30
            ELSE 0 
          END AS orderdate
  FROM dbo.Nums
  WHERE n <= @numorders
  ORDER BY CHECKSUM(NEWID());

CREATE CLUSTERED INDEX idx_cl_od ON dbo.Orders(orderdate);

CREATE NONCLUSTERED INDEX idx_nc_sid_od_i_cid
  ON dbo.Orders(shipperid, orderdate)
  INCLUDE(custid);

CREATE UNIQUE INDEX idx_unc_od_oid_i_cid_eid
  ON dbo.Orders(orderdate, orderid)
  INCLUDE(custid, empid);

ALTER TABLE dbo.Orders ADD
  CONSTRAINT PK_Orders PRIMARY KEY NONCLUSTERED(orderid),
  CONSTRAINT FK_Orders_Customers
    FOREIGN KEY(custid)    REFERENCES dbo.Customers(custid),
  CONSTRAINT FK_Orders_Employees
    FOREIGN KEY(empid)     REFERENCES dbo.Employees(empid),
  CONSTRAINT FK_Orders_Shippers
    FOREIGN KEY(shipperid) REFERENCES dbo.Shippers(shipperid);
GO

快速建成1--100000数值表的语句

DECLARE @max AS INT, @rc AS INT;
SET @max = 1000000;
SET @rc = 1;

INSERT INTO dbo.Nums(n) VALUES(1);
WHILE @rc * 2 <= @max
BEGIN
INSERT INTO dbo.Nums(n) SELECT n + @rc FROM dbo.Nums;
SET @rc = @rc * 2;
END

INSERT INTO dbo.Nums(n)
SELECT n + @rc FROM dbo.Nums WHERE n + @rc <= @max;
GO

生成随机custId,empId,shipperid 的语句

1+ABS(CHECKSUM(NEWID())%@NUMBERMAX 生成 1--->@NUMBERMAX内随机整数

INSERT INTO dbo.Orders(orderid, custid, empid, shipperid, orderdate)
SELECT n AS orderid,
    'C' + RIGHT('000000000'
            + CAST(
                1 + ABS(CHECKSUM(NEWID())) % @numcusts
                AS VARCHAR(10)), 10) AS custid,
    1 + ABS(CHECKSUM(NEWID())) % @numemps AS empid,
    CHAR(ASCII('A') - 2
           + 2 * (1 + ABS(CHECKSUM(NEWID())) % @numshippers)) AS shipperid,
      DATEADD(day, n / (@numorders / (@numyears * 365.25)), @startdate)
        -- late arrival with earlier date

　　　---在这个例子中是生成随机数是四年,四年有只有一个闰年,平均每年365.25天,这样跟据订单号可以算出每个订单大约放在哪一天,每个订单号为10倍的时候作了一些处理,+-31天,所以10倍的订单号有可能出现在上个月
        - CASE WHEN n % 10 = 0
            THEN 1 + ABS(CHECKSUM(NEWID())) % 30
            ELSE 0
          END AS orderdate
FROM dbo.Nums
WHERE n <= @numorders
ORDER BY CHECKSUM(NEWID());

优化方法论

返回系统里的等待信息

返回系统的等待信息

1 SELECT
2   wait_type,
3   waiting_tasks_count,
4   wait_time_ms,
5   max_wait_time_ms,
6   signal_wait_time_ms
7 FROM sys.dm_os_wait_stats
8 ORDER BY wait_type;

signal_wait_time_ms 表示从线程收到资源可用信号开始到得到CPU时间,开始资源为止经历的时间,如果这个属性很高,就表明CPU有问题.

分离重量级的等待

分离重量级的等待

-- Isolate top waits
WITH Waits AS
(
  SELECT
    wait_type,
    wait_time_ms / 1000. AS wait_time_s,
    100. * wait_time_ms / SUM(wait_time_ms) OVER() AS pct,
    ROW_NUMBER() OVER(ORDER BY wait_time_ms DESC) AS rn,
    100. * signal_wait_time_ms / wait_time_ms as signal_pct
  FROM sys.dm_os_wait_stats
  WHERE wait_time_ms > 0
    AND wait_type NOT LIKE N'%SLEEP%'
    AND wait_type NOT LIKE N'%IDLE%'
    AND wait_type NOT LIKE N'%QUEUE%'    
    AND wait_type NOT IN(  N'CLR_AUTO_EVENT'
                         , N'REQUEST_FOR_DEADLOCK_SEARCH'
                         , N'SQLTRACE_BUFFER_FLUSH'
                         /* filter out additional irrelevant waits */ )
)
SELECT
  W1.wait_type, 
  CAST(W1.wait_time_s AS NUMERIC(12, 2)) AS wait_time_s,
  CAST(W1.pct AS NUMERIC(5, 2)) AS pct,
  CAST(SUM(W2.pct) AS NUMERIC(5, 2)) AS running_pct,
  CAST(W1.signal_pct AS NUMERIC(5, 2)) AS signal_pct
FROM Waits AS W1
  JOIN Waits AS W2
    ON W2.rn <= W1.rn
GROUP BY W1.rn, W1.wait_type, W1.wait_time_s, W1.pct, W1.signal_pct
HAVING SUM(W2.pct) - W1.pct < 80 -- percentage threshold
    OR W1.rn <= 5
ORDER BY W1.rn;
GO

这个语句返回累计等待时间(从最大的等待时间的等待类型向下加)占总等待时间达80%的等待类型或等待时间为前5位的等待类型

收集等待信息

这个可以使用SQL SERVER中的功能 Server Actity 来实现

也可以用一张表来不间断的收集当前的累计等待时间,通过计算差值来算出间隔内的等待时间(Interval Wait Time)

创建WaitStats收集表

USE Performance;
IF OBJECT_ID('dbo.WaitStats', 'U') IS NOT NULL DROP TABLE dbo.WaitStats;

CREATE TABLE dbo.WaitStats
(
  dt                  DATETIME     NOT NULL DEFAULT (CURRENT_TIMESTAMP),
  wait_type           NVARCHAR(60) NOT NULL,
  waiting_tasks_count BIGINT       NOT NULL,
  wait_time_ms        BIGINT       NOT NULL,
  max_wait_time_ms    BIGINT       NOT NULL,
  signal_wait_time_ms BIGINT       NOT NULL
);

定义一个时间间隔的任务(比如1小时),运行下面代码,填充收集表

-- Load waitstats data on regular intervals
INSERT INTO Performance.dbo.WaitStats
    (wait_type, waiting_tasks_count, wait_time_ms,
     max_wait_time_ms, signal_wait_time_ms)
  SELECT
    wait_type, waiting_tasks_count, wait_time_ms,
    max_wait_time_ms, signal_wait_time_ms
  FROM sys.dm_os_wait_stats
  WHERE wait_type NOT IN (N'MISCELLANEOUS');

创建下列函数,处理数据收集表,返回间隔等待信息

-- Creation script for IntervalWaits function
IF OBJECT_ID('dbo.IntervalWaits', 'IF') IS NOT NULL
  DROP FUNCTION dbo.IntervalWaits;
GO

CREATE FUNCTION dbo.IntervalWaits
  (@fromdt AS DATETIME, @todt AS DATETIME)
RETURNS TABLE
AS

RETURN
  WITH Waits AS
  (
    SELECT dt, wait_type, wait_time_ms,
      ROW_NUMBER() OVER(PARTITION BY wait_type
                        ORDER BY dt) AS rn
    FROM dbo.WaitStats
  )
  SELECT Prv.wait_type, Prv.dt AS start_time,
    CAST((Cur.wait_time_ms - Prv.wait_time_ms)
           / 1000. AS NUMERIC(12, 2)) AS interval_wait_s
  FROM Waits AS Cur
    JOIN Waits AS Prv
      ON Cur.wait_type = Prv.wait_type
      AND Cur.rn = Prv.rn + 1
      AND Prv.dt >= @fromdt
      AND Prv.dt < DATEADD(day, 1, @todt)
GO

可以使用简单的查询来分析间隔等待时间,比如下面的查询,返回间隔内的新增等待时间,且按区间内的总新增时间倒序

使用收集表,按区间内所有间隔新增时间总和倒序显示

SELECT wait_type, start_time, interval_wait_s
FROM dbo.IntervalWaits('20090212', '20090213') AS F
ORDER BY SUM(interval_wait_s) OVER(PARTITION BY wait_type) DESC,
  wait_type, start_time;
GO

也可以将函数返回的表放在Excel中,通过Excel生成数据透视图来查看新增等待时间信息

提供给Excel的数据视图

-- Prepare view for pivot table
IF OBJECT_ID('dbo.IntervalWaitsSample', 'V') IS NOT NULL
  DROP VIEW dbo.IntervalWaitsSample;
GO

CREATE VIEW dbo.IntervalWaitsSample
AS

SELECT wait_type, start_time, interval_wait_s
FROM dbo.IntervalWaits('20090212', '20090213') AS F;
GO

细化到数据库/文件级别

分析数据库IO

-- Analyze DB IO
WITH DBIO AS
(
  SELECT
    DB_NAME(IVFS.database_id) AS db,
    MF.type_desc,
    SUM(IVFS.num_of_bytes_read + IVFS.num_of_bytes_written) AS io_bytes,
    SUM(IVFS.io_stall) AS io_stall_ms
  FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS IVFS
    JOIN sys.master_files AS MF
      ON IVFS.database_id = MF.database_id
      AND IVFS.file_id = MF.file_id
  GROUP BY DB_NAME(IVFS.database_id), MF.type_desc
)
SELECT db, type_desc, 
  CAST(1. * io_bytes / (1024 * 1024) AS NUMERIC(12, 2)) AS io_mb,
  CAST(io_stall_ms / 1000. AS NUMERIC(12, 2)) AS io_stall_s,
  CAST(100. * io_stall_ms / SUM(io_stall_ms) OVER()
       AS NUMERIC(10, 2)) AS io_stall_pct,
  ROW_NUMBER() OVER(ORDER BY io_stall_ms DESC) AS rn
FROM DBIO
ORDER BY io_stall_ms DESC;

细化到进程级别

直接使用SQL SERVER PROFILER GUI会有一些性能问题,因为输出会同时到目标文件和客户端,可以由GUI生成TSQL 脚本如下

针对生产环镜中的工作负荷跟踪有时需要几小时,有的却要几天.

SQL TRACE跟踪脚本过程

---------------------------------------------------------------------
-- Trace Performance Workload
---------------------------------------------------------------------

SET NOCOUNT ON;
USE master;
GO

IF OBJECT_ID('dbo.PerfworkloadTraceStart', 'P') IS NOT NULL
  DROP PROC dbo.PerfworkloadTraceStart;
GO

CREATE PROC dbo.PerfworkloadTraceStart
  @dbid      AS INT,
  @tracefile AS NVARCHAR(245),
  @traceid   AS INT OUTPUT
AS

-- Create a Queue
DECLARE @rc          AS INT;
DECLARE @maxfilesize AS BIGINT;

SET @maxfilesize = 5;

EXEC @rc = sp_trace_create @traceid OUTPUT, 0, @tracefile, @maxfilesize, NULL 
IF (@rc != 0) GOTO error;

-- Set the events
DECLARE @on AS BIT;
SET @on = 1;

-- RPC:Completed
exec sp_trace_setevent @traceid, 10, 15, @on;
exec sp_trace_setevent @traceid, 10, 8, @on;
exec sp_trace_setevent @traceid, 10, 16, @on;
exec sp_trace_setevent @traceid, 10, 48, @on;
exec sp_trace_setevent @traceid, 10, 1, @on;
exec sp_trace_setevent @traceid, 10, 17, @on;
exec sp_trace_setevent @traceid, 10, 10, @on;
exec sp_trace_setevent @traceid, 10, 18, @on;
exec sp_trace_setevent @traceid, 10, 11, @on;
exec sp_trace_setevent @traceid, 10, 12, @on;
exec sp_trace_setevent @traceid, 10, 13, @on;
exec sp_trace_setevent @traceid, 10, 6, @on;
exec sp_trace_setevent @traceid, 10, 14, @on;

-- SP:Completed
exec sp_trace_setevent @traceid, 43, 15, @on;
exec sp_trace_setevent @traceid, 43, 8, @on;
exec sp_trace_setevent @traceid, 43, 48, @on;
exec sp_trace_setevent @traceid, 43, 1, @on;
exec sp_trace_setevent @traceid, 43, 10, @on;
exec sp_trace_setevent @traceid, 43, 11, @on;
exec sp_trace_setevent @traceid, 43, 12, @on;
exec sp_trace_setevent @traceid, 43, 13, @on;
exec sp_trace_setevent @traceid, 43, 6, @on;
exec sp_trace_setevent @traceid, 43, 14, @on;

-- SP:StmtCompleted
exec sp_trace_setevent @traceid, 45, 8, @on;
exec sp_trace_setevent @traceid, 45, 16, @on;
exec sp_trace_setevent @traceid, 45, 48, @on;
exec sp_trace_setevent @traceid, 45, 1, @on;
exec sp_trace_setevent @traceid, 45, 17, @on;
exec sp_trace_setevent @traceid, 45, 10, @on;
exec sp_trace_setevent @traceid, 45, 18, @on;
exec sp_trace_setevent @traceid, 45, 11, @on;
exec sp_trace_setevent @traceid, 45, 12, @on;
exec sp_trace_setevent @traceid, 45, 13, @on;
exec sp_trace_setevent @traceid, 45, 6, @on;
exec sp_trace_setevent @traceid, 45, 14, @on;
exec sp_trace_setevent @traceid, 45, 15, @on;

-- SQL:BatchCompleted
exec sp_trace_setevent @traceid, 12, 15, @on;
exec sp_trace_setevent @traceid, 12, 8, @on;
exec sp_trace_setevent @traceid, 12, 16, @on;
exec sp_trace_setevent @traceid, 12, 48, @on;
exec sp_trace_setevent @traceid, 12, 1, @on;
exec sp_trace_setevent @traceid, 12, 17, @on;
exec sp_trace_setevent @traceid, 12, 6, @on;
exec sp_trace_setevent @traceid, 12, 10, @on;
exec sp_trace_setevent @traceid, 12, 14, @on;
exec sp_trace_setevent @traceid, 12, 18, @on;
exec sp_trace_setevent @traceid, 12, 11, @on;
exec sp_trace_setevent @traceid, 12, 12, @on;
exec sp_trace_setevent @traceid, 12, 13, @on;

-- SQL:StmtCompleted
exec sp_trace_setevent @traceid, 41, 15, @on;
exec sp_trace_setevent @traceid, 41, 8, @on;
exec sp_trace_setevent @traceid, 41, 16, @on;
exec sp_trace_setevent @traceid, 41, 48, @on;
exec sp_trace_setevent @traceid, 41, 1, @on;
exec sp_trace_setevent @traceid, 41, 17, @on;
exec sp_trace_setevent @traceid, 41, 10, @on;
exec sp_trace_setevent @traceid, 41, 18, @on;
exec sp_trace_setevent @traceid, 41, 11, @on;
exec sp_trace_setevent @traceid, 41, 12, @on;
exec sp_trace_setevent @traceid, 41, 13, @on;
exec sp_trace_setevent @traceid, 41, 6, @on;
exec sp_trace_setevent @traceid, 41, 14, @on;

-- Set the Filters

-- Application name filter
EXEC sp_trace_setfilter @traceid, 10, 0, 7, N'SQL Server Profiler%';
-- Database ID filter
EXEC sp_trace_setfilter @traceid, 3, 0, 0, @dbid;

-- Set the trace status to start
EXEC sp_trace_setstatus @traceid, 1;

-- Print trace id and file name for future references
PRINT 'Trace ID: ' + CAST(@traceid AS VARCHAR(10))
  + ', Trace File: ''' + @tracefile + '.trc''';

GOTO finish;

error: 
PRINT 'Error Code: ' + CAST(@rc AS VARCHAR(10));

finish: 
GO

启动跟踪

View Code

-- Start the trace
DECLARE @dbid AS INT, @traceid AS INT;
SET @dbid = DB_ID('Performance');

EXEC master.dbo.PerfworkloadTraceStart
  @dbid      = @dbid,
  @tracefile = 'c:\temp\Perfworkload 20090212',
  @traceid   = @traceid OUTPUT;
GO

停止跟踪

停止和关闭跟踪

-- Stop the trace (assuming trace id was 2)
EXEC sp_trace_setstatus 2, 0;
EXEC sp_trace_setstatus 2, 2;
GO

分析跟跟数据,使用fn_trace_gettable函数把跟踪文件加载到表

加载跟踪文件进表

-- Load trace data to table
SET NOCOUNT ON;
USE Performance;
IF OBJECT_ID('dbo.Workload', 'U') IS NOT NULL DROP TABLE dbo.Workload;
GO

SELECT CAST(TextData AS NVARCHAR(MAX)) AS tsql_code,
  Duration AS duration
INTO dbo.Workload
FROM sys.fn_trace_gettable('c:\temp\Perfworkload 20090212.trc', NULL) AS T
WHERE Duration > 0
  AND EventClass IN(41, 45);
GO

分析跟踪表

-- Aggregate trace data by query
SELECT
  tsql_code,
  SUM(duration) AS total_duration
FROM dbo.Workload
GROUP BY tsql_code;

缓存中的查询计划,和上面的SQL TRACE方法不同的是,这里不包含查询计划不在缓存中的查询(例如查询或过程使用的RECOMPILE项时)

DMV查询统计

-- Query Statistics
SELECT TOP (5)
  MAX(query) AS sample_query,
  SUM(execution_count) AS cnt,
  SUM(total_worker_time) AS cpu,
  SUM(total_physical_reads) AS reads,
  SUM(total_logical_reads) AS logical_reads,
  SUM(total_elapsed_time) AS duration
FROM (SELECT 
        QS.*,
        SUBSTRING(ST.text, (QS.statement_start_offset/2) + 1,
           ((CASE statement_end_offset 
              WHEN -1 THEN DATALENGTH(ST.text)
              ELSE QS.statement_end_offset END 
                  - QS.statement_start_offset)/2) + 1
        ) AS query
      FROM sys.dm_exec_query_stats AS QS
        CROSS APPLY sys.dm_exec_sql_text(QS.sql_handle) AS ST
        CROSS APPLY sys.dm_exec_plan_attributes(QS.plan_handle) AS PA
      WHERE PA.attribute = 'dbid'
        AND PA.value = DB_ID('Performance')) AS D
GROUP BY query_hash
ORDER BY duration DESC;

物理读: 由硬盘上的块读到缓存中,每读一个块就是一个物理读

逻辑读: 从缓存中每读一行就是一次逻辑读

所以要测量查询的I/O信息需要先清空缓存

要查看查询的运行时间还要先清空缓存中的执行计划

查看查询IO信息

-- First clear cache
DBCC DROPCLEANBUFFERS;

-- Then run
SET STATISTICS IO ON;

SELECT orderid, custid, empid, shipperid, orderdate, filler
FROM dbo.Orders
WHERE orderdate >= '20080101'
  AND orderdate < '20080201';
GO

SET STATISTICS IO OFF;
GO

查看查询的运行时间

---------------------------------------------------------------------
-- Measuring Runtime of Queries
---------------------------------------------------------------------

-- STATISTICS TIME

-- First clear cache
DBCC DROPCLEANBUFFERS;
DBCC FREEPROCCACHE;

-- Then run
SET STATISTICS TIME ON;

SELECT orderid, custid, empid, shipperid, orderdate, filler
FROM dbo.Orders
WHERE orderdate >= '20080101'
  AND orderdate < '20080201';

SET STATISTICS TIME OFF;
GO