SELECT ATC.OWNER,
       ATC.TABLE_NAME,
       UTC.COMMENTS,
       ATC.COLUMN_NAME,
       ATC.DATA_TYPE,
       ATC.DATA_LENGTH,
       ATC.NULLABLE,
       UCC.COMMENTS
  FROM (SELECT ATC.OWNER,
               ATC.TABLE_NAME,
               ATC.COLUMN_NAME,
               ATC.DATA_TYPE,
               ATC.DATA_LENGTH,
               ATC.NULLABLE
          FROM ALL_TAB_COLUMNS ATC
         WHERE ATC.OWNER IN ('GTJA21')) ATC
  LEFT OUTER JOIN USER_COL_COMMENTS UCC
    ON ATC.TABLE_NAME = UCC.TABLE_NAME
   AND ATC.COLUMN_NAME = UCC.COLUMN_NAME
  LEFT OUTER JOIN USER_TAB_COMMENTS UTC
    ON ATC.TABLE_NAME = UTC.TABLE_NAME
 ORDER BY ATC.TABLE_NAME,
          ATC.COLUMN_NAME

          --多个用户下的表明細+表注釋+字段明細+字段注釋

 SELECT ATC.OWNER,
                   ATC.TABLE_NAME,
                   ATC.COLUMN_NAME,
                   UTC.COMMENTS,
                   ATC.DATA_TYPE,
                   ATC.DATA_LENGTH,
                   ATC.NULLABLE,
                   UCC.COMMENTS
              FROM (SELECT ATC.OWNER,
                           ATC.TABLE_NAME,
                           ATC.COLUMN_NAME,
                           ATC.DATA_TYPE,
                           ATC.DATA_LENGTH,
                           ATC.NULLABLE
                      FROM ALL_TAB_COLUMNS ATC
                     WHERE ATC.OWNER IN ('UserName1', 'UserName2')) ATC
              LEFT OUTER JOIN ALL_COL_COMMENTS UCC
                ON ATC.TABLE_NAME = UCC.TABLE_NAME
               AND ATC.COLUMN_NAME = UCC.COLUMN_NAME
              LEFT OUTER JOIN ALL_TAB_COMMENTS UTC
                ON ATC.TABLE_NAME = UTC.TABLE_NAME
             ORDER BY ATC.TABLE_NAME, ATC.COLUMN_NAME