Class VirtualColumnNode

  • All Implemented Interfaces:
    Visitable

    class VirtualColumnNode
    extends ValueNode
    A VirtualColumnNode represents a virtual column reference to a column in a row returned by an underlying ResultSetNode. The underlying column could be in a base table, view (which could expand into a complex expression), subquery in the FROM clause, temp table, expression result, etc. By the time we get to code generation, all VirtualColumnNodes should stand only for references to columns in a base table within a FromBaseTable.
    • Field Detail

      • columnId

        int columnId
      • correlated

        private boolean correlated
    • Constructor Detail

      • VirtualColumnNode

        VirtualColumnNode​(ResultSetNode sourceResultSet,
                          ResultColumn sourceColumn,
                          int columnId,
                          ContextManager cm)
                   throws StandardException
        Constructor for a VirtualColumnNode.
        Parameters:
        sourceResultSet - The ResultSetNode where the value is originating
        sourceColumn - The ResultColumn where the value is originating
        columnId - The columnId within the current Row
        cm - The context manager
        Throws:
        StandardException
    • Method Detail

      • printSubNodes

        void printSubNodes​(int depth)
        Prints the sub-nodes of this object. See QueryTreeNode.java for how tree printing is supposed to work.
        Overrides:
        printSubNodes in class QueryTreeNode
        Parameters:
        depth - The depth of this node in the tree
      • getSourceResultSet

        ResultSetNode getSourceResultSet()
        Return the ResultSetNode that is the source of this VirtualColumnNode.
        Returns:
        ResultSetNode
      • getSourceColumn

        ResultColumn getSourceColumn()
        Return the ResultColumn that is the source of this VirtualColumnNode.
        Returns:
        ResultSetNode
      • getTableName

        java.lang.String getTableName()
        Get the name of the table the ResultColumn is in, if any. This will be null if the user did not supply a name (for example, select a from t). The method will return B for this example, select b.a from t as b The method will return T for this example, select t.a from t
        Overrides:
        getTableName in class ValueNode
        Returns:
        A String containing the name of the table the Column is in. If the column is not in a table (i.e. is a derived column), it returns NULL.
      • getSchemaName

        java.lang.String getSchemaName()
                                throws StandardException
        Get the name of the schema the ResultColumn's table is in, if any. The return value will be null if the user did not supply a schema name (for example, select t.a from t). Another example for null return value (for example, select b.a from t as b). But for following query select app.t.a from t, this will return APP
        Overrides:
        getSchemaName in class ValueNode
        Returns:
        A String containing the name of the schema for the Column's table. If the column is not in a schema (i.e. derived column), it returns NULL.
        Throws:
        StandardException
      • updatableByCursor

        public boolean updatableByCursor()
        Return whether or not the ResultColumn is wirtable by a positioned update.
        Overrides:
        updatableByCursor in class ValueNode
        Returns:
        TRUE, if the column is a base column of a table and is writable by a positioned update.
      • setCorrelated

        void setCorrelated()
        Mark this VCN as a reference to a correlated column. (It's source resultSet is an outer ResultSet.
      • getCorrelated

        boolean getCorrelated()
        Return whether or not this VCN is a correlated reference.
        Returns:
        Whether or not this VCN is a correlated reference.
      • isCloneable

        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.
      • generateExpression

        void generateExpression​(ExpressionClassBuilder acb,
                                MethodBuilder mb)
                         throws StandardException
        ColumnNode's are against the current row in the system. This lets us generate a faster get that simply returns the column from the current row, rather than getting the value out and returning that, only to have the caller (in the situations needed) stuffing it back into a new column holder object. We will assume the general generate() path is for getting the value out, and use generateColumn() when we want to keep the column wrapped.
        Overrides:
        generateExpression in class ValueNode
        Parameters:
        acb - The ExpressionClassBuilder for the class being built
        mb - The method the expression will go into
        Throws:
        StandardException - Thrown on error
      • getOrderableVariantType

        protected int getOrderableVariantType()
                                       throws StandardException
        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 (constant expressions)
        Overrides:
        getOrderableVariantType in class ValueNode
        Returns:
        The variant type for the underlying expression.
        Throws:
        StandardException - thrown on error
      • getTypeServices

        public final DataTypeDescriptor getTypeServices()
        Get the DataTypeServices from this Node.
        Overrides:
        getTypeServices in class ValueNode
        Returns:
        The DataTypeServices from this Node. This may be null if the node isn't bound yet.
      • isEquivalent

        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:

        • 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.
        Throws:
        StandardException