com.akiban.sql.parser
Class SpecialFunctionNode

java.lang.Object
  com.akiban.sql.parser.QueryTreeNode
      com.akiban.sql.parser.ValueNode
          com.akiban.sql.parser.SpecialFunctionNode

All Implemented Interfaces:

Visitable

public class SpecialFunctionNode
extends ValueNode

SpecialFunctionNode handles system SQL functions. A function value is either obtained by a method call off the LanguageConnectionContext or Activation. LanguageConnectionContext functions are state related to the connection. Activation functions are those related to the statement execution. Each SQL function takes no arguments and returns a SQLvalue.

Functions supported:

• USER
• CURRENT_USER
• CURRENT_ROLE
• SESSION_USER
• SYSTEM_USER
• CURRENT SCHEMA
• CURRENT ISOLATION
• IDENTITY_VAL_LOCAL

This node is used rather than some use of MethodCallNode for runtime performance. MethodCallNode does not provide a fast access to the current language connection or activatation, since it is geared towards user defined routines.

Field Summary

Fields inherited from class com.akiban.sql.parser.QueryTreeNode

AUTOINCREMENT_CREATE_MODIFY, AUTOINCREMENT_INC_INDEX, AUTOINCREMENT_IS_AUTOINCREMENT_INDEX, AUTOINCREMENT_START_INDEX

Constructor Summary

SpecialFunctionNode()

Method Summary

protected boolean	isEquivalent(ValueNode o) Tests if this node is equivalent to the specified ValueNode.
String	toString() Convert this object to a String.

Methods inherited from class com.akiban.sql.parser.ValueNode

copyFrom, getColumnName, getSchemaName, getSourceResultColumn, getTableName, getType, getTypeId, init, isBinaryEqualsOperatorNode, isBooleanFalse, isBooleanTrue, isConstantExpression, isInListProbeNode, isParameterNode, isRelationalOperator, isSameNodeType, setNullability, setType

Methods inherited from class com.akiban.sql.parser.QueryTreeNode

accept, convertDefaultNode, debugFlush, debugPrint, formatNodeString, getBeginOffset, getDebugOutput, getEndOffset, getNodeFactory, getNodeType, getNullNode, getParserContext, getStatementType, getUserData, init, init, init, init, init, init, init, init, init, init, init, init, init, isInstanceOf, makeTableName, makeTableName, nodeHeader, printLabel, printSubNodes, setBeginOffset, setDebugOutput, setEndOffset, setNodeType, setParserContext, setUserData, stackPrint, treePrint, treePrint, treePrint

Methods inherited from class java.lang.Object

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

Constructor Detail

SpecialFunctionNode

public SpecialFunctionNode()

Method Detail

toString

public String toString()

Description copied from class: ValueNode

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

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:

• The two ValueNodes must be of the same node type to be considered equivalent. e.g.: CastNode vs. CastNode - equivalent (if their args also match), ColumnReference vs CastNode - not equivalent.
• If node P contains other ValueNode(s) and so on, those node(s) must also be of the same node type to be considered equivalent.
• If node P takes a parameter list, then the number of arguments and its arguments for the two nodes must also match to be considered equivalent. e.g.: CAST(c1 as INTEGER) vs CAST(c1 as SMALLINT), they are not equivalent.
• When comparing SQL NULLs in this context, they are considered to be equivalent.
• If this does not apply or it is determined that the two nodes are not equivalent then the derived class of this method should return false; otherwise, return true.

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.