@Override
  protected void defineColumns(StringBuilder query) {
    if (sourceTab != null) {
      query.append("(");
      List<String> columnDescs = getColumnDescs();
      query.append(StringUtils.join(columnDescs, ','));
      query.append(") ");
    }
  }
Define columns of the create query.
ql/src/java/org/apache/hadoop/hive/ql/txn/compactor/CompactionQueryBuilderForInsertOnly.java