【文件属性】：
文件名称：SQL Server Execution Plans Second Edition
文件大小：7.32MB
文件格式：PDF
更新时间：2021-11-07 04:25:22
SQLServer
Every day, out in the various discussion boards devoted to Microsoft SQL Server, the
same types of questions come up repeatedly:
• Why is this query running slow?
• Is SQL Server using my index?
• Why isn't SQL Server using my index?
• Why does this query run faster than this query?
• And so on (and on).
The correct response is probably different in each case, but in order to arrive at the
answer you have to ask the same return question every time: have you looked at the
execution plan?
Execution plans show you what's going on behind the scenes in SQL Server. They can
provide you with a wealth of information on how SQL Server is executing your queries,
including the points below.
• Which indexes are getting used, and where no indexes are being used at all.
• How the data is being retrieved, and joined, from the tables defined in your query.
• How aggregations in GROUP BY queries are put together.
• The anticipated load, and the estimated cost, that all these operations place upon
the system.
All this information makes the execution plan a fairly important tool in the tool belt of
database administrator, database developers, report writers, developers, and pretty much
anyone who writes T-SQL to access data in a SQL Server database.