org.apache.derby.impl.sql.compile
Class VerifyAggregateExpressionsVisitor

java.lang.Object
  org.apache.derby.impl.sql.compile.VerifyAggregateExpressionsVisitor

All Implemented Interfaces:

Visitor

public class VerifyAggregateExpressionsVisitor
extends java.lang.Object
implements Visitor

If a RCL (SELECT list) contains an aggregate, then we must verify that the RCL (SELECT list) is valid. For ungrouped queries, the RCL must be composed entirely of valid aggregate expressions - in this case, no column references outside of an aggregate. For grouped aggregates, the RCL must be composed of grouping columns or valid aggregate expressions - in this case, the only column references allowed outside of an aggregate are grouping columns.

Field Summary

private GroupByList

groupByList

Constructor Summary

VerifyAggregateExpressionsVisitor(GroupByList groupByList)

Method Summary

boolean	skipChildren(Visitable node) Don't visit children under an aggregate, subquery or any node which is equivalent to any of the group by expressions.
boolean	stopTraversal() Method that is called to see if query tree traversal should be stopped before visiting all nodes.
Visitable	visit(Visitable node) Verify that this expression is ok for an aggregate query.
boolean	visitChildrenFirst(Visitable node) Method that is called to see if visit() should be called on the children of node before it is called on node itself.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

groupByList

private GroupByList groupByList

Constructor Detail

VerifyAggregateExpressionsVisitor

public VerifyAggregateExpressionsVisitor(GroupByList groupByList)

Method Detail

visit

public Visitable visit(Visitable node)
                throws StandardException

Verify that this expression is ok for an aggregate query.

Specified by:

visit in interface Visitor

Parameters:

node - the node to process

Returns:

me

Throws:

StandardException - on ColumnReference not in group by list, ValueNode or JavaValueNode that isn't under an aggregate

skipChildren

public boolean skipChildren(Visitable node)
                     throws StandardException

Don't visit children under an aggregate, subquery or any node which is equivalent to any of the group by expressions.

Specified by:

skipChildren in interface Visitor

Parameters:

node - the node to process

Returns:

true/false

Throws:

StandardException

stopTraversal

public boolean stopTraversal()

Description copied from interface: Visitor

Method that is called to see if query tree traversal should be stopped before visiting all nodes. Useful for short circuiting traversal if we already know we are done.

Specified by:

stopTraversal in interface Visitor

Returns:

true/false

visitChildrenFirst

public boolean visitChildrenFirst(Visitable node)

Description copied from interface: Visitor

Method that is called to see if visit() should be called on the children of node before it is called on node itself. If this method always returns true, the visitor will walk the tree bottom-up. If it always returns false, the tree is visited top-down.

Specified by:

visitChildrenFirst in interface Visitor

Parameters:

node - the top node of a sub-tree about to be visited

Returns:

true if node's children should be visited before node, false otherwise