Class SpecialFunctionNode

java.lang.Object
org.apache.derby.impl.sql.compile.QueryTreeNode
org.apache.derby.impl.sql.compile.ValueNode
org.apache.derby.impl.sql.compile.SpecialFunctionNode
All Implemented Interfaces:
Visitable
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 activation, since it is geared towards user defined routines.

  • Field Details

  • Constructor Details

    • SpecialFunctionNode

      SpecialFunctionNode(int kind, ContextManager cm)

  • Method Details

    • bindExpression

      ValueNode bindExpression(FromList fromList, SubqueryList subqueryList, List<AggregateNode> aggregates) throws StandardException
      Binding this special function means setting the result DataTypeServices. In this case, the result type is based on the operation requested.
      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. Not used in this case.
      aggregates - The aggregate list being built as we find AggregateNodes. Not used in this case.
      Returns:
      The new top of the expression tree.
      Throws:
      StandardException - Thrown on error

    • getOrderableVariantType

      protected int getOrderableVariantType()
      Return the variant type for the underlying expression. All supported special functions are QUERY_INVARIANT
      Overrides:
      getOrderableVariantType in class ValueNode
      Returns:
      The variant type for the underlying expression.

    • generateExpression

      void generateExpression(ExpressionClassBuilder acb, MethodBuilder mb) throws StandardException
      Generate an expression that returns a DataValueDescriptor and calls a method off the language connection or the activation.
      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

    • 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

    • isSameNodeKind

      boolean isSameNodeKind(ValueNode o)
      Description copied from class: ValueNode
      Some node classes represent several logical node types (to reduce footprint), which we call kinds. This means that implementations of ValueNode.isEquivalent(ValueNode) cannot always just use instanceof to check if the other node represents the same kind. Hence this method needs to be overridden by all node classes that represent several kinds. This default implementation does not look at kinds. It is only called from implementations of isEquivalent.
      Overrides:
      isSameNodeKind in class ValueNode
      Parameters:
      o - The other value node whose kind we want to compare with.
      Returns:
      true if this and o represent the same logical node type, i.e. kind.

    • isEquivalent

      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.