user_constraints,user_cons_columns
Oracle 查看一个表对应的主键和外键的约束关系，查看的语句：
select a.owner 主键拥有者
,a.table_name 主键表
,b.column_name 主键列
,C.OWNER 外键拥有者
,c.table_name 外键表
,d.column_name 外键列
from user_constraints a
left join user_cons_columns b
on a.constraint_name=b.constraint_name
left join user_constraints C
ON C.R_CONSTRAINT_NAME=a.constraint_name
left join user_cons_columns d
on c.constraint_name=d.constraint_name
where a.constraint_type='P'
and a.table_name='XXX' --需要查看主外键关系的表
order by a.table_name
宁外的一种写法
select
a.owner 外键拥有者,
a.table_name 外键表,
substr(c.column_name,1,127) 外键列,
b.owner 主键拥有者,
b.table_name 主键表,
substr(d.column_name,1,127) 主键列
from
user_constraints a,
user_constraints b,
user_cons_columns c,
user_cons_columns d
where
a.r_constraint_name=b.constraint_name
and a.constraint_type='R'
and b.constraint_type='P'
and a.r_owner=b.owner
and a.constraint_name=c.constraint_name
and b.constraint_name=d.constraint_name
and a.owner=c.owner
and a.table_name=c.table_name
and b.owner=d.owner
and b.table_name=d.table_name
数据字典表列说明：
desc user_constraints
| Name | Comments |
| OWNER | 表的所有者 |
| CONSTRAINT_NAME | 约束名 |
| CONSTRAINT_TYPE | 约束类型 |
| TABLE_NAME | Name associated with table with constraint definition |
| SEARCH_CONDITION | Text of search condition for table check |
| R_OWNER | Owner of table used in referential constraint |
| R_CONSTRAINT_NAME | Name of unique constraint definition for referenced table |
| DELETE_RULE | The delete rule for a referential constraint |
| STATUS | Enforcement status of constraint - ENABLED or DISABLED |
| DEFERRABLE | Is the constraint deferrable - DEFERRABLE or NOT DEFERRABLE |
| DEFERRED | Is the constraint deferred by default - DEFERRED or IMMEDIATE |
| VALIDATED | Was this constraint system validated? - VALIDATED or NOT VALIDATED |
| GENERATED | Was the constraint name system generated? - GENERATED NAME or USERNAME |
| BAD | Creating this constraint should give ORA-02436. Rewrite it before2000 AD. |
| RELY | If set, this flag will be used in optimizer |
| LAST_CHANGE | The date when this column was last enabled or disabled |
| INDEX_OWNER | The owner of the index used by the constraint |
| INDEX_NAME | The index used by the constraint |
| INVALID | |
| VIEW_RELATED |
desc user_cons_columns;
| Name | Default Comments |
| OWNER | Owner of the constraint definition |
| CONSTRAINT_NAME | Name associated with the constraint definition |
| TABLE_NAME | Name associated with table with constraint definition |
| COLUMN_NAME | Name associated with column or attribute of object column specified in the constraint definition |
| POSITION | Original position of column or attribute in definition |
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