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

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.ConstantNode
All Implemented Interfaces:
Visitable
Direct Known Subclasses:
BitConstantNode, BooleanConstantNode, CharConstantNode, NumericConstantNode, SQLBooleanConstantNode, UntypedNullConstantNode, UserTypeConstantNode, XMLConstantNode

abstract class ConstantNode
extends ValueNode

ConstantNode holds literal constants as well as nulls.

A NULL from the parser may not yet know its type; that must be set during binding, as it is for parameters.

the DataValueDescriptor methods want to throw exceptions when they are of the wrong type, but to do that they must check typeId when the value is null, rather than the instanceof check they do for returning a valid value.

For code generation, we generate a static field. Then we set the field be the proper constant expression (something like getDatavalueFactory().getCharDataValue("hello", ...)) ) in the constructor of the generated method. Ideally we would have just


Field Summary
(package private)  DataValueDescriptor value
           
 
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
ConstantNode()
          Constructor for untyped nodes, which contain little information
 
Method Summary
 ValueNode bindExpression(FromList fromList, SubqueryList subqueryList, java.util.Vector aggregateVector)
          Bind this expression.
 boolean constantExpression(PredicateList whereClause)
          Return whether or not this expression tree represents a constant value.
(package private) abstract  void generateConstant(ExpressionClassBuilder acb, MethodBuilder mb)
          This generates the proper constant.
 void generateExpression(ExpressionClassBuilder acb, MethodBuilder mb)
          For a ConstantNode, we generate the equivalent literal value.
 ValueNode getClone()
          Return a clone of this node.
protected  int getOrderableVariantType()
          Return the variant type for the underlying expression.
 DataValueDescriptor getValue()
          Get the value in this ConstantNode
 void init(java.lang.Object typeId, java.lang.Object nullable, java.lang.Object maximumWidth)
          Initializer for non-numeric types
 boolean isCloneable()
          Return whether or not this expression tree is cloneable.
 boolean isConstantExpression()
          Return whether or not this expression tree represents a constant expression.
protected  boolean isEquivalent(ValueNode o)
          Tests if this node is equivalent to the specified ValueNode.
(package private)  boolean isNull()
          Return whether or not this node represents a typed null constant.
(package private)  void setValue(DataValueDescriptor value)
          Set the value in this ConstantNode.
 java.lang.String toString()
          Convert this object to a String.
 
Methods inherited from class org.apache.derby.impl.sql.compile.ValueNode
bindExpression, categorize, changeToCNF, checkIsBoolean, checkTopPredicatesForEqualsConditions, copyFields, eliminateNots, evaluateConstantExpressions, genEqualsFalseTree, generate, generateFilter, genIsNullTree, genSQLJavaSQLTree, getColumnName, getConstantValueAsObject, getDataValueFactory, getSchemaName, getSourceResultColumn, getTableName, getTablesReferenced, getTransformed, getTypeCompiler, getTypeId, getTypeServices, init, isBinaryEqualsOperatorNode, isBooleanFalse, isBooleanTrue, isInListProbeNode, isParameterNode, isRelationalOperator, isSameNodeType, optimizableEqualityNode, preprocess, putAndsOnTop, remapColumnReferencesToExpressions, requiresTypeFromContext, selectivity, setCollationInfo, setCollationInfo, setCollationUsingCompilationSchema, setCollationUsingCompilationSchema, setNullability, setTransformed, setType, setType, setType, 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, 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
 

Field Detail

value

DataValueDescriptor value
Constructor Detail

ConstantNode

ConstantNode()
Constructor for untyped nodes, which contain little information

Method Detail

init

public void init(java.lang.Object typeId,
                 java.lang.Object nullable,
                 java.lang.Object maximumWidth)
          throws StandardException
Initializer for non-numeric types

Overrides:
init in class QueryTreeNode
Parameters:
typeId - The Type ID of the datatype
nullable - True means the constant is nullable
maximumWidth - The maximum number of bytes in the data value
Throws:
StandardException

setValue

void setValue(DataValueDescriptor value)
Set the value in this ConstantNode.


getValue

public DataValueDescriptor getValue()
Get the value in this ConstantNode


toString

public java.lang.String toString()
Convert this object to a String. See comments in QueryTreeNode.java for how this should be done for tree printing.

Overrides:
toString in class ValueNode
Returns:
This object as a String

isCloneable

public boolean isCloneable()
Return whether or not this expression tree is cloneable.

Overrides:
isCloneable in class ValueNode
Returns:
boolean Whether or not this expression tree is cloneable.

getClone

public ValueNode getClone()
Return a clone of this node.

Overrides:
getClone in class ValueNode
Returns:
ValueNode A clone of this node.

bindExpression

public ValueNode bindExpression(FromList fromList,
                                SubqueryList subqueryList,
                                java.util.Vector aggregateVector)
                         throws StandardException
Bind this expression. This means binding the sub-expressions, as well as figuring out what the return type is for this expression. In this case, there are no sub-expressions, and the return type is already known, so this is just a stub.

Overrides:
bindExpression in class ValueNode
Parameters:
fromList - The FROM list for the query this expression is in, for binding columns.
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. Although this class doesn't throw this exception, it's subclasses do and hence this method signature here needs to have throws StandardException

isConstantExpression

public boolean isConstantExpression()
Return whether or not this expression tree represents a constant expression.

Overrides:
isConstantExpression in class ValueNode
Returns:
Whether or not this expression tree represents a constant expression.

constantExpression

public boolean constantExpression(PredicateList whereClause)
Description copied from class: ValueNode
Return whether or not this expression tree represents a constant value. In this case, "constant" means that it will always evaluate to the same thing, even if it includes columns. A column is constant if it is compared to a constant expression.

Overrides:
constantExpression in class ValueNode
Returns:
True means this expression tree represents a constant value.
See Also:
ValueNode.constantExpression(org.apache.derby.impl.sql.compile.PredicateList)

generateExpression

public void generateExpression(ExpressionClassBuilder acb,
                               MethodBuilder mb)
                        throws StandardException
For a ConstantNode, we generate the equivalent literal value. A null is generated as a Null value cast to the type of the constant node. The subtypes of ConstantNode generate literal expressions for non-null values.

Overrides:
generateExpression in class ValueNode
Parameters:
acb - The ExpressionClassBuilder for the class being built
mb - The method the code to place the code
Throws:
StandardException - Thrown on error

generateConstant

abstract void generateConstant(ExpressionClassBuilder acb,
                               MethodBuilder mb)
                        throws StandardException
This generates the proper constant. It is implemented by every specific constant node (e.g. IntConstantNode).

Parameters:
acb - The ExpressionClassBuilder for the class being built
mb - The method the code to place the code
Throws:
StandardException - Thrown on error

isNull

boolean isNull()
Return whether or not this node represents a typed null constant.


getOrderableVariantType

protected int getOrderableVariantType()
Return the variant type for the underlying expression. The variant type can be: VARIANT - variant within a scan (method calls and non-static field access) SCAN_INVARIANT - invariant within a scan (column references from outer tables) QUERY_INVARIANT - invariant within the life of a query VARIANT - immutable

Overrides:
getOrderableVariantType in class ValueNode
Returns:
The variant type for the underlying expression.

isEquivalent

protected boolean isEquivalent(ValueNode o)
                        throws StandardException
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.
Throws:
StandardException

Built on Thu 2011-03-10 11:54:14+0000, from revision ???

Apache Derby V10.6 Internals - Copyright © 2004,2007 The Apache Software Foundation. All Rights Reserved.