Class CurrentRowLocationNode

  • All Implemented Interfaces:
    Visitable

    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.
    • Constructor Detail

      • CurrentRowLocationNode

        CurrentRowLocationNode​(ContextManager cm)
    • Method Detail

      • bindExpression

        ValueNode bindExpression​(FromList fromList,
                                 SubqueryList subqueryList,
                                 java.util.List<AggregateNode> aggregates)
                          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
        aggregates - The aggregate list being built as we find AggregateNodes
        Returns:
        The new top of the expression tree.
        Throws:
        StandardException - Thrown on error
      • generateExpression

        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; ... protected 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

        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.