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 Details

    • sourceResultSet

      private ResultSetNode sourceResultSet
    • sourceColumn

      private ResultColumn sourceColumn
    • columnId

      int columnId
    • correlated

      private boolean correlated
  • Constructor Details

    • 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 Details

    • 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

      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

      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.
    • getSourceResultColumn

      ResultColumn getSourceResultColumn()
      Return the ResultColumn that is the source of this VirtualColumnNode.
      Overrides:
      getSourceResultColumn in class ValueNode
      Returns:
      ResultSetNode
    • 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.
    • setType

      public final void setType(DataTypeDescriptor dtd) throws StandardException
      Description copied from class: ValueNode
      Set the DataTypeServices for this ValueNode. This method is overridden in ParameterNode.
      Overrides:
      setType in class ValueNode
      Parameters:
      dtd - The DataTypeServices to set in this ValueNode
      Throws:
      StandardException
    • 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