可以参考下：
SELECT
S1.NAME AS 表名,
S2.NAME AS 列名,
S2."TYPE$" AS 字段类型,
S2."LENGTH$" AS 字段长度
FROM
SYSOBJECTS S1,
SYSCOLUMNS S2
WHERE
S1."SUBTYPE$" = 'UTAB'
AND S1.ID = S2.ID;

测试下这个查询，看看是否符合需要

SELECT /*+ CASE_WHEN_CVT_IFUN(8)*/
       USR.NAME AS USER_NAME
      ,SCH.NAME AS SCHEMA_NAME
      ,TAB.NAME AS TABLE_NAME
      ,COL.COLID + 1 AS COLUMN_ID
      ,COL.NAME AS COLUMN_NAME
      ,SF_GET_TYPE_WITH_LENGTH(COL.TYPE$, COL.LENGTH$, COL.SCALE) AS DATATYPE 
      ,CAST(CASE WHEN COL.TYPE$ IN ('NUMERIC','NUMBER','DEC','DECIMAL') THEN 22
                 WHEN COL.SCALE = 7 AND UNICODE() = 1 THEN COL.LENGTH$ * 4 
                 WHEN COL.SCALE = 7 AND UNICODE() = 0 THEN COL.LENGTH$ * 2
             ELSE COL.LENGTH$ END 
            AS NUMBER
           ) AS DATA_LENGTH
      ,CAST(CASE WHEN COL.TYPE$ IN ('NUMERIC','NUMBER','DEC','DECIMAL') THEN CASE WHEN COL.LENGTH$ = 0 THEN NULL ELSE COL.LENGTH$ END 
                 WHEN COL.TYPE$ IN ('INTERVAL YEAR TO MONTH','INTERVAL YEAR','INTERVAL MONTH','INTERVAL DAY','INTERVAL DAY TO HOUR','INTERVAL DAY TO MINUTE','INTERVAL DAY TO SECOND','INTERVAL HOUR','INTERVAL HOUR TO MINUTE','INTERVAL HOUR TO SECOND','INTERVAL MINUTE','INTERVAL MINUTE TO SECOND','INTERVAL SECOND') THEN ((COL.SCALE & 0XF0)>>4) 
             END 
            AS NUMBER
           ) AS DATA_PRECISION
      ,CAST(CASE WHEN COL.TYPE$ IN ('NUMERIC','NUMBER','DEC','DECIMAL') AND COL.LENGTH$=0 THEN NULL 
                 WHEN COL.TYPE$ IN ('INTERVAL YEAR TO MONTH','INTERVAL YEAR','INTERVAL MONTH','INTERVAL DAY','INTERVAL DAY TO HOUR','INTERVAL DAY TO MINUTE','INTERVAL DAY TO SECOND','INTERVAL HOUR','INTERVAL HOUR TO MINUTE','INTERVAL HOUR TO SECOND','INTERVAL MINUTE','INTERVAL MINUTE TO SECOND','INTERVAL SECOND') THEN (COL.SCALE & 0X0F) 
                 ELSE COL.SCALE 
             END 
            AS NUMBER
           ) AS DATA_SCALE       
      ,COL.NULLABLE$ AS NULLALBE
      ,COL.DEFVAL AS DATADEFAULT
      ,CASE WHEN SF_COL_IS_IDX_KEY(IDXINFO.KEYNUM, IDXINFO.KEYINFO, COL.COLID) = 1 THEN 'Y' END AS PRIMARY_KEY
      ,CASE WHEN COL.INFO2 & 0x01 = 1 AND LENGTH(TAB.INFO6) > 24 THEN DECODE(SUBSTRBB(TAB.INFO6,25,1),1,'IDENTITY',2,'AUTO_INCREMENT') END AS INCREMENT_TYPE
      ,COLCOMM.COMMENT$ AS COMMENTS
  FROM SYSOBJECTS TAB
  JOIN SYSOBJECTS SCH                 ON SCH.TYPE$ = 'SCH' AND SCH.ID = TAB.SCHID
  JOIN SYSOBJECTS USR                 ON USR.TYPE$ = 'UR' AND USR.ID = SCH.PID
  JOIN SYSCOLUMNS COL                 ON COL.ID = TAB.ID
  LEFT JOIN SYSCOLUMNCOMMENTS COLCOMM ON COLCOMM.SCHNAME = SCH.NAME AND COLCOMM.TVNAME = TAB.NAME AND COLCOMM.COLNAME = COL.NAME
  LEFT JOIN SYSCONS CONS              ON CONS.TYPE$ = 'P' AND CONS.TABLEID = TAB.ID
  LEFT JOIN SYSINDEXES IDXINFO        ON IDXINFO.ID = CONS.INDEXID 
 --WHERE SCH.NAME = '模式名'
 --  AND TAB.NAME = '表名' 
 ORDER BY 1,2,3,4