Oracle获取表字段名，字段类型，字段长度，注释

SELECT b.comments as 注释,
       a.column_name as 列名,
       a.data_type || \'(\' || a.data_length || \')\' as 数据类型,
       a.nullable as 是否为空
  FROM user_tab_columns a, user_col_comments b
 WHERE a.TABLE_NAME = \'表名\'
   and b.table_name = \'表名\'
   and a.column_name = b.column_name