Class PushProjector
Pushing is particularly interesting in the case of join, because there are multiple inputs. Generally an expression can be pushed down to a particular input if it depends upon no other inputs. If it can be pushed down to both sides, it is pushed down to the left.
Sometimes an expression needs to be split before it can be pushed down. To flag that an expression cannot be split, specify a rule that it must be preserved. Such an expression will be pushed down intact to one of the inputs, or not pushed down at all.

Nested Class Summary
Modifier and TypeClassDescriptionstatic interface
A functor that replies true or false for a given expression. 
Constructor Summary
ConstructorDescriptionPushProjector
(@Nullable Project origProj, @Nullable RexNode origFilter, RelNode childRel, PushProjector.ExprCondition preserveExprCondition, RelBuilder relBuilder) Creates a PushProjector object for pushing projects past a RelNode. 
Method Summary
Modifier and TypeMethodDescription@Nullable RelNode
convertProject
(@Nullable RexNode defaultExpr) Decomposes a projection to the input references referenced by a projection and a filter, either of which is optional.convertRefsAndExprs
(RexNode rex, List<RelDataTypeField> destFields, int[] adjustments) Clones an expression tree and walks through it, adjusting each RexInputRef index by some amount, and converting expressions that need to be preserved to field references.createNewProject
(RelNode projChild, int[] adjustments) Creates a new projection based on the original projection, adjusting all input refs using an adjustment array passed in.createProjectRefsAndExprs
(RelNode projChild, boolean adjust, boolean rightSide) Creates a projection based on the inputs specified in a bitmap and the expressions that need to be preserved.int[]
Determines how much each input reference needs to be adjusted as a result of projection.boolean
Locates all references found in either the projection expressions a filter, as well as references to expressions that should be preserved.

Constructor Details

PushProjector
public PushProjector(@Nullable Project origProj, @Nullable RexNode origFilter, RelNode childRel, PushProjector.ExprCondition preserveExprCondition, RelBuilder relBuilder) Creates a PushProjector object for pushing projects past a RelNode. Parameters:
origProj
 the original projection that is being pushed; may be null if the projection is implied as a result of a projection having been trivially removedorigFilter
 the filter that the projection must also be pushed past, if applicablechildRel
 the RelNode that the projection is being pushed pastpreserveExprCondition
 condition for whether an expression should be preserved in the projection


Method Details

convertProject
Decomposes a projection to the input references referenced by a projection and a filter, either of which is optional. If both are provided, the filter is underneath the project.Creates a projection containing all input references as well as preserving any special expressions. Converts the original projection and/or filter to reference the new projection. Then, finally puts on top, a final projection corresponding to the original projection.
 Parameters:
defaultExpr
 expression to be used in the projection if no fields or special columns are selected Returns:
 the converted projection if it makes sense to push elements of the projection; otherwise returns null

locateAllRefs
public boolean locateAllRefs()Locates all references found in either the projection expressions a filter, as well as references to expressions that should be preserved. Based on that, determines whether pushing the projection makes sense. Returns:
 true if all inputs from the child that the projection is being pushed past are referenced in the projection/filter and no special preserve expressions are referenced; in that case, it does not make sense to push the projection

createProjectRefsAndExprs
Creates a projection based on the inputs specified in a bitmap and the expressions that need to be preserved. The expressions are appended after the input references. Parameters:
projChild
 child that the projection will be created on top ofadjust
 if true, need to create new projection expressions; otherwise, the existing ones are reusedrightSide
 if true, creating a projection for the right hand side of a join Returns:
 created projection

getAdjustments
public int[] getAdjustments()Determines how much each input reference needs to be adjusted as a result of projection. Returns:
 array indicating how much each input needs to be adjusted by

convertRefsAndExprs
public RexNode convertRefsAndExprs(RexNode rex, List<RelDataTypeField> destFields, int[] adjustments) Clones an expression tree and walks through it, adjusting each RexInputRef index by some amount, and converting expressions that need to be preserved to field references. Parameters:
rex
 the expressiondestFields
 fields that the new expressions will be referencingadjustments
 the amount each input reference index needs to be adjusted by Returns:
 modified expression tree

createNewProject
Creates a new projection based on the original projection, adjusting all input refs using an adjustment array passed in. If there was no original projection, create a new one that selects every field from the underlying rel.If the resulting projection would be trivial, return the child.
 Parameters:
projChild
 child of the new projectadjustments
 array indicating how much each input reference should be adjusted by Returns:
 the created projection
