做个笔记，仅供参考
decode(a.NULLABLE,'Y','0','1') notNull,//是否允许空
COALESCE(m.COMMENTS,' ') comments,//字段备注
decode(k.uniqueness,'UNIQUE','1','0') uniques,//是否唯一
COALESCE(k.index_name,' ') indexName,//如果是索引，索引名
decode(k.key,'0') masterKey//是否主键
FROM
user_tab_columns a
INNER JOIN user_tables d on a.TABLE_NAME=d.TABLE_NAME
LEFT JOIN user_tab_comments t ON t.TABLE_NAME=d.TABLE_NAME
LEFT JOIN user_col_comments m ON m.COLUMN_NAME=a.COLUMN_NAME AND m.TABLE_NAME=d.TABLE_NAME
LEFT JOIN
(
SELECT e.index_name,u.TABLE_NAME,u.COLUMN_NAME,e.uniqueness,decode(p.constraint_name,NULL,'N','Y') key
from user_indexes e INNER JOIN user_ind_columns u ON e.index_name=u.index_name
LEFT JOIN ( select constraint_name from user_constraints where constraint_type='P' ) p ON e.index_name=p.constraint_name
) k ON k.TABLE_NAME=a.TABLE_NAME and k.COLUMN_NAME=a.COLUMN_NAME
ORDER BY tbName
