Package org.apache.derby.impl.sql.compile

Class BaseColumnNode

  • All Implemented Interfaces:
    Visitable
    class BaseColumnNode
extends ValueNode
    A BaseColumnNode represents a column in a base table. The parser generates a BaseColumnNode for each column reference. A column refercence could be a column in a base table, a column in a view (which could expand into a complex expression), or a column in a subquery in the FROM clause. By the time we get to code generation, all BaseColumnNodes should stand only for columns in base tables.

    • Field Detail

      • columnName

        private java.lang.String columnName

    • Constructor Detail

      • BaseColumnNode

        BaseColumnNode​(java.lang.String columnName,
               TableName tableName,
               DataTypeDescriptor dtd,
               ContextManager cm)
        throws StandardException
        Constructor for a referenced column name
        Parameters:
        columnName - The name of the column being referenced
        tableName - The qualification for the column
        dtd - Data type descriptor for the column
        cm - Context manager
        Throws:
        StandardException

    • Method Detail

      • 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

      • getColumnName

        java.lang.String getColumnName()
        Get the name of this column
        Overrides:
        getColumnName in class ValueNode
        Returns:
        The name of this column

      • getTableName

        java.lang.String getTableName()
        Get the user-supplied table name of this column. 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:
        The user-supplied name of this column. Null if no user- supplied name.

      • getSchemaName

        java.lang.String getSchemaName()
                        throws StandardException
        Get the user-supplied schema name for this column's table. This will be null if the user did not supply a 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:
        The schema name for this column's table
        Throws:
        StandardException

      • 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 (constant expressions)
        Overrides:
        getOrderableVariantType in class ValueNode
        Returns:
        The variant type for the underlying expression.

      • isEquivalent

        boolean isEquivalent​(ValueNode o)
        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.

      • acceptChildren

        void acceptChildren​(Visitor v)
             throws StandardException
        Description copied from class: QueryTreeNode
        Accept a visitor on all child nodes. All sub-classes that add fields that should be visited, should override this method and call accept(v) on all visitable fields, as well as super.acceptChildren(v) to make sure all visitable fields defined by the super-class are accepted too.
        Overrides:
        acceptChildren in class QueryTreeNode
        Parameters:
        v - the visitor
        Throws:
        StandardException - on errors raised by the visitor