May 2019
Intermediate to advanced
484 pages
11h 23m
English
Content preview from Learn T-SQL Querying
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Plans with lookups
One of the quickest ways to tune a query is to add a covering index. As we discussed in Chapter 4, Exploring Query Execution Plans, the presence of a lookup in a query execution plan indicates that a query is not covered. We can leverage this same XQuery method to find query execution plans that contain a lookup anywhere in the plan.
The following query will find query execution plans that have a lookup:
WITH XMLNAMESPACES(DEFAULT'http://schemas.microsoft.com/sqlserver/2004/07/showplan'), Lookupsearch AS (SELECT qp.query_plan, cp.usecounts, ls.query('.') AS StmtSimple, cp.plan_handle FROM sys.dm_exec_cached_plans cp (NOLOCK) CROSS APPLY sys.dm_exec_query_plan(cp.plan_handle) qp CROSS APPLY qp.query_plan.nodes('//StmtSimple') ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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