Microsoft SQL Server 2012 Bible

Understanding Execution Plan Operators

SQL server uses many different operators when creating execution plans. Some represent specific physical tasks, whereas most logically represent a collection of hidden tasks. Many of these operators are related to specific statements types — statements that you may rarely see. Others are much more common.

Table 44.1 lists the key operators regarding select queries and indexing.

Table 44.1 Query Execution Plan Operators

Icon	Definition	Description
	Clustered index scan	In a clustered index scan, SQL Server reads the entire clustered index — typically sequentially — but it can be otherwise depending on the isolation level and the fragmentation. SQL Server chooses this operation when the set of rows requested by the WHERE clause or JOIN condition is a large percentage of rows needed from the table or no index is available to select the range.
	Table scan	A table scan is similar to a clustered index scan but scans a heap.
	Clustered index seek	In a clustered index seek, SQL Server navigates the clustered index B-tree to retrieve specific rows. The benefit of the clustered index seek is that when the rows are determined, all the columns are immediately ...