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

java.lang.Object
  extended by org.apache.derby.impl.sql.compile.QueryTreeNode
      extended by org.apache.derby.impl.sql.compile.ValueNode
          extended by org.apache.derby.impl.sql.compile.CurrentRowLocationNode
All Implemented Interfaces:
Visitable

public class CurrentRowLocationNode
extends ValueNode

The CurrentRowLocation operator is used by DELETE and UPDATE to get the RowLocation of the current row for the target table. The bind() operations for DELETE and UPDATE add a column to the target list of the SelectNode that represents the ResultSet to be deleted or updated.


Field Summary
 
Fields inherited from class org.apache.derby.impl.sql.compile.ValueNode
transformed
 
Fields inherited from class org.apache.derby.impl.sql.compile.QueryTreeNode
AUTOINCREMENT_CREATE_MODIFY, AUTOINCREMENT_INC_INDEX, AUTOINCREMENT_IS_AUTOINCREMENT_INDEX, AUTOINCREMENT_START_INDEX, isPrivilegeCollectionRequired
 
Constructor Summary
CurrentRowLocationNode()
           
 
Method Summary
 ValueNode bindExpression(FromList fromList, SubqueryList subqueryList, java.util.Vector aggregateVector)
          Binding this expression means setting the result DataTypeServices.
 void generateExpression(ExpressionClassBuilder acb, MethodBuilder mbex)
          CurrentRowLocationNode is used in updates and deletes.
protected  boolean isEquivalent(ValueNode o)
          Tests if this node is equivalent to the specified ValueNode.
 
Methods inherited from class org.apache.derby.impl.sql.compile.ValueNode
bindExpression, categorize, changeToCNF, checkIsBoolean, checkTopPredicatesForEqualsConditions, constantExpression, copyFields, eliminateNots, evaluateConstantExpressions, genEqualsFalseTree, generate, generateFilter, genIsNullTree, genSQLJavaSQLTree, getClone, getColumnName, getConstantValueAsObject, getDataValueFactory, getOrderableVariantType, getSchemaName, getSourceResultColumn, getTableName, getTablesReferenced, getTransformed, getTypeCompiler, getTypeId, getTypeServices, init, isBinaryEqualsOperatorNode, isBooleanFalse, isBooleanTrue, isCloneable, isConstantExpression, isInListProbeNode, isParameterNode, isRelationalOperator, isSameNodeType, optimizableEqualityNode, preprocess, putAndsOnTop, remapColumnReferencesToExpressions, requiresTypeFromContext, selectivity, setCollationInfo, setCollationInfo, setCollationUsingCompilationSchema, setCollationUsingCompilationSchema, setNullability, setTransformed, setType, setType, setType, toString, updatableByCursor, verifyChangeToCNF, verifyEliminateNots, verifyPutAndsOnTop
 
Methods inherited from class org.apache.derby.impl.sql.compile.QueryTreeNode
accept, acceptChildren, bindOffsetFetch, bindRowMultiSet, bindUserType, checkReliability, checkReliability, convertDefaultNode, createTypeDependency, debugFlush, debugPrint, disablePrivilegeCollection, formatNodeString, foundString, generateAuthorizeCheck, getBeginOffset, getClassFactory, getCompilerContext, getContextManager, getCursorInfo, getDataDictionary, getDependencyManager, getEndOffset, getExecutionFactory, getGenericConstantActionFactory, getIntProperty, getLanguageConnectionContext, getNodeFactory, getNodeType, getNullNode, getParameterTypes, getRowEstimate, getSchemaDescriptor, getSchemaDescriptor, getStatementType, getTableDescriptor, getTypeCompiler, init, init, init, init, init, init, init, init, init, init, init, init, init, isAtomic, isInstanceOf, isPrivilegeCollectionRequired, isSessionSchema, isSessionSchema, makeConstantAction, makeTableName, makeTableName, nodeHeader, orReliability, parseStatement, printLabel, printSubNodes, referencesSessionSchema, resolveTableToSynonym, setBeginOffset, setContextManager, setEndOffset, setNodeType, setRefActionInfo, stackPrint, treePrint, treePrint, verifyClassExist
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

CurrentRowLocationNode

public CurrentRowLocationNode()
Method Detail

bindExpression

public ValueNode bindExpression(FromList fromList,
                                SubqueryList subqueryList,
                                java.util.Vector aggregateVector)
                         throws StandardException
Binding this expression means setting the result DataTypeServices. In this case, the result type is always the same.

Overrides:
bindExpression in class ValueNode
Parameters:
fromList - The FROM list for the statement. This parameter is not used in this case.
subqueryList - The subquery list being built as we find SubqueryNodes
aggregateVector - The aggregate vector being built as we find AggregateNodes
Returns:
The new top of the expression tree.
Throws:
StandardException - Thrown on error

generateExpression

public void generateExpression(ExpressionClassBuilder acb,
                               MethodBuilder mbex)
                        throws StandardException
CurrentRowLocationNode is used in updates and deletes. See generate() in UpdateNode and DeleteNode to get the full overview of generate(). This class is responsible for generating the method that will return the RowLocation for the next row to be updated or deleted. This routine will generate a method of the form: private SQLRef fieldx; ... public DataValueDescriptor exprx() throws StandardException { return fieldx = ( "result set member".getRowLocation(), fieldx); } and return the generated code: exprx() ("result set member" is a member of the generated class added by UpdateNode or DeleteNode.) This exprx function is used within another exprx function, and so doesn't need a static field or to be public; but at present, it has both. fieldx is a generated field that is initialized to null when the activation is constructed. getSQLRef will re-use fieldx on calls after the first call, rather than allocate a new SQLRef for each call.

Overrides:
generateExpression in class ValueNode
Parameters:
acb - The ExpressionClassBuilder for the class being built
mbex - The method the expression will go into
Throws:
StandardException - Thrown on error

isEquivalent

protected boolean isEquivalent(ValueNode o)
Description copied from class: ValueNode
Tests if this node is equivalent to the specified ValueNode. Two ValueNodes are considered equivalent if they will evaluate to the same value during query execution.

This method provides basic expression matching facility for the derived class of ValueNode and it is used by the language layer to compare the node structural form of the two expressions for equivalence at bind phase.

Note that it is not comparing the actual row values at runtime to produce a result; hence, when comparing SQL NULLs, they are considered to be equivalent and not unknown.

One usage case of this method in this context is to compare the select column expression against the group by expression to check if they are equivalent. e.g.:

SELECT c1+c2 FROM t1 GROUP BY c1+c2

In general, node equivalence is determined by the derived class of ValueNode. But they generally abide to the rules below:

Specified by:
isEquivalent in class ValueNode
Parameters:
o - the node to compare this ValueNode against.
Returns:
true if the two nodes are equivalent, false otherwise.

Built on Thu 2010-12-23 20:49:13+0000, from revision ???

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