1.查看前10行

-- 老版本
SELECT * FROM 表 WHERE ROWNUM <= 10;

-- 12c+
SELECT * FROM 表 FETCH FIRST 10 ROWS ONLY;

2.查询指定表的字段及其备注

SELECT COLUMN_NAME, COMMENTS
FROM USER_COL_COMMENTS
WHERE TABLE_NAME = UPPER('表名');

进阶：查看字段、数据类型、备注

SELECT
  t.COLUMN_NAME  字段名,
  t.DATA_TYPE    数据类型,
  c.COMMENTS     字段注释
FROM USER_TAB_COLUMNS t
LEFT JOIN USER_COL_COMMENTS c
  ON t.TABLE_NAME  = c.TABLE_NAME
 AND t.COLUMN_NAME = c.COLUMN_NAME
WHERE t.TABLE_NAME = UPPER('你的表名');