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Shortcut: Compare query plans in SQL Server Management Studio

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[数据库(mssql) 所属分类 数据库(mssql) | 发布者 店小二03 | 时间 2018 | 作者 红领巾 ] 0人收藏点击收藏

One of the advantages of SQL Server Management Studio (SSMS) is that it can be used to analyze queries, not just to execute them.

There are two basic types of query plan: estimated execution plans, and actual execution plans.

For a typical query, I can obtain the estimated execution plan, by hitting Ctrl-L, choosing the option in the Query menu, or clicking on the toolbar icon:


Shortcut: Compare query plans in SQL Server Management Studio

Let's do this for the following query:


Shortcut: Compare query plans in SQL Server Management Studio

We get the following plan output:


Shortcut: Compare query plans in SQL Server Management Studio

Now we might look at this plan and wonder if we exerted control over how the joins were performed, if we'd improve things. Perhaps we'd heard that merge joins were more efficient and thought SQL Server should have used those.

Now we can change the query like this:


Shortcut: Compare query plans in SQL Server Management Studio

Notice I've added the word MERGE between INNER and JOIN in this query. But how do we know what SQL Server thinks? We can get another estimated query plan but what we really want is to compare them.

When we obtain an estimated plan for multiple queries at once, SSMS shows us a comparison of the two, by showing us the proportion of the overall query for each part. (Perhaps we shouldn't force that change :blush:)


Shortcut: Compare query plans in SQL Server Management Studio

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