SQL Server: Key Lookup Operator: When your nonclustered index doesn’t cover all the data required by the select query it jumps to cluster index to get the data. Non Clustered Index Seek (without Key Lookup): When your non clustered index cover all the data required by select query then the operator which have greater chance to come in execution plan is Non Clustered Index(without Key lookup) This reflect that Key Lookup is a very expensive operation compare to NC Index Seek(without key lookup) because it perform a IO to clustered index the from clustered to heap to get the data which is not covered by nonclutered index. Let’s stimulate a situation where we get lookup operator
Posted on: Mon, 14 Jul 2014 04:17:53 +0000
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