oracle中如何查询所有用户表的表名、主键名称、索引及外键等

select t.*,i.index_type from user_ind_columns t,user_indexes i where t.index_name = i.index_name and t.table_name = i.table_name and t.table_name = 要查询的表 

select cu.* from user_cons_columns cu, user_constraints au where cu.constraint_name = au.constraint_name and au.constraint_type = 'P' and au.table_name = 要查询的表 

select column_name from user_cons_columns cu, user_constraints au where cu.constraint_name = au.constraint_name and au.constraint_type = 'U' and au.table_name = 要查询的表 

select * from user_constraints c where c.constraint_type = 'R' and c.table_name = 要查询的表 

select * from user_cons_columns cl where cl.constraint_name = 外键名称 

select * from user_cons_columns cl where cl.constraint_name = 外键引用表的键名 

select t.*,c.COMMENTS from user_tab_columns t,user_col_comments c where t.table_name = c.table_name and t.column_name = c.column_name and t.table_name = 要查询的表

select a.constraint_name,  a.column_name 
from user_cons_columns a, user_constraints b 
where a.constraint_name = b.constraint_name 
and b.constraint_type = 'P' and a.table_name = '大写的表名'

alter table 表名 add constraint 主键名 primary key(列名);

​​​​​​​alter table 表名 drop constraint 主键名;