C# Class System.Data.Entity.Core.Query.PlanCompiler.ProjectionPruner

DistinctOp We remove all null and constant keys that are not referenced as long as there is one key left. We add all remaining keys to the referenced list and proceed to the inputs

ElementOp An ElementOp that is still present when Projection Prunning is invoked can only get introduced in the TransformationRules phase by transforming an apply operation into a scalar subquery. Such ElementOp serves as root of a defining expression of a VarDefinitionOp node and thus what it produces is useful.

ExistsOp The child must be a ProjectOp - with exactly 1 var. Mark it as referenced

FilterOp First visit the predicate (because that may contain references to the relop input), and then visit the relop input. No additional processing is required

First defer to default handling for groupby nodes If all group aggregate vars are prunned out turn it into a GroupBy.

MultiStreamNestOp Insist (for now) that all Vars are required

PhysicalProjectOp Insist that all Vars in this are required

ProjectOp We visit the projections first (the VarDefListOp child), and then the input (the RelOp child) - this reverse order is necessary, since the projections need to be visited to determine if anything from the input is really needed. The VarDefListOp child will handle the removal of unnecessary VarDefOps. On the way out, we then update our "Vars" property to reflect the Vars that have been eliminated

SingleStreamNestOp Insist (for now) that all Vars are required

UnnestOp Marks the unnestVar as referenced, and if there is a child, visits the child.

VarDefListOp Walks the children (VarDefOp), and looks for those whose Vars have been referenced. Only those VarDefOps are visited - the others are ignored. At the end, a new list of children is created - with only those VarDefOps that have been referenced

VarRefOp Mark the corresponding Var as "referenced"

ApplyOps Common handling for all ApplyOps. Visit the right child first to capture any references to the left, and then visit the left child.

Visits the children and recomputes the node info

Visits the children in reverse order and recomputes the node info

GroupByBase First, we visit the vardeflist for aggregates and potentially group aggregates as they may reference keys (including constant keys). Then we remove all null and constant keys that are not referenced as long as there is one key left. We add all remaining key columns to the referenced list. Then we walk through the vardeflist for the keys; and finally process the relop input Once we're done, we update the "Outputs" varset - to account for any pruned vars. The "Keys" varset will not change

JoinOps Common handling for all join ops. For all joins (other than crossjoin), we must first visit the predicate (to capture any references from it), and then visit the relop inputs. The relop inputs can be visited in any order because there can be no correlations between them For crossjoins, we simply use the default processing - visit all children ; there can be no correlations between the nodes anyway

NestOps Common handling for all NestOps.

SetOps Common handling for all SetOps. We first identify the "output" vars that are referenced, and mark the corresponding "input" vars as referenced We then remove all unreferenced output Vars from the "Outputs" varset as well as from the Varmaps. Finally, we visit the children

SortOp First visit the sort keys - no sort key can be eliminated. Then process the vardeflist child (if there is one) that contains computed vars, and finally process the relop input. As before, the computedvars and sortkeys need to be processed before the relop input

Adds a reference to each var in a set of Vars

Adds a reference to this Var

Is this Var referenced?

Is this var unreferenced?

The real driver of the pruning process. Simply invokes the visitor over the input node

Runs through the given subtree, and eliminates all unreferenced expressions

Runs through the root node of the tree, and eliminates all unreferenced expressions

Trivial private constructor

Prunes a VarMap - gets rid of unreferenced vars from the VarMap inplace Additionally, propagates var references to the inner vars

Prunes a varset - gets rid of unreferenced vars from the Varset in place

Helper method for removing redundant constant keys from GroupByOp and DistictOp. It only examines the keys defined in the given varDefListNode. It removes all constant and null keys that are not referenced elsewhere, but ensuring that at least one key is left. It should not be called with empty keyVec.