16. Using the Query Optimizer : Types of Nodes in a QEP : Non-Join Nodes in a QEP : Projection-Restriction Nodes
 
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Projection-Restriction Nodes
A projection-restriction (proj-rest) node describes the result of a projection and/or WHERE clause restriction applied to a subsidiary node. It defines how a subsidiary node is to key into the table and what qualification to use on the table. This type of node displays the following:
A label identifying it as a proj-rest node
Storage structure (which is usually heap)
Total number of pages and tuples
Query cost information
Optionally, sort information (whether the data produced by this node is already sorted or requires sorting)
For a description of each of these parts of the display, see Information on a QEP.
Proj-rest nodes are used to remove data irrelevant to the query from a table, so that the minimum amount of data is carried around during the execution of the query. Therefore, only those columns referenced in the target list and WHERE clause for a table are projected, and only those rows that satisfy the WHERE clause restrictions are retained for use higher in the plan.
All you see is the amount of disk I/O required to read the appropriate rows from the node below, and that amount depends on what storage structures were used and the number of pages accessed.