public static SemanticNodeProcessor getTableScanMapJoin() {
    return new TableScanMapJoinProcessor();
  }
Merge the current task with the task for the current mapjoin. The mapjoin operator
has already been encountered.

@param op
         operator being processed
@param oldTask
         the old task for the current mapjoin
@param opProcCtx
         processing context
@param pos
         position of the parent in the stack
ql/src/java/org/apache/hadoop/hive/ql/optimizer/MapJoinFactory.java