Oracle主键和外键相关知识

SCOTT@ORA12C> create table emp_1 as select * from emp; --附表
Table created.
SCOTT@ORA12C> create table dept_1 as select * from dept; --主表
Table created.
SCOTT@ORA12C> alter table dept_1 add constraint PK_DEPT_1 primary key(deptno); --主表添加主键约束
Table altered.
SCOTT@ORA12C> alter table emp_1 add constraint FK_EMP_1 foreign key(deptno) references dept_1(deptno);
Table altered. --添加外键约束

查询表的索引键值情况：

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 IN ('DEPT_1', 'EMP_1') --需要查看主外键关系的表
16   ORDER BY a.table_name;
OWNER    TABLE_NAME    COLUMN_NAM OWNER  TABLE_NAME  COLUMN_NAM
---------- --------------- ---------- ---------- --------------- ----------
SCOTT    DEPT_1    DEPTNO     SCOTT  EMP_1   DEPTNO
1 row selected.

通过以上发现dept_1和emp_1 列deptno主外键关系。
如果删除dept_1的数据，那么必须对附表emp_1进行全表扫描：
以下语句可以查询：那些外键没有索引:

SELECT TABLE_NAME,
CONSTRAINT_NAME,
CNAME1 || NVL2(CNAME2, ',' || CNAME2, NULL) ||
NVL2(CNAME3, ',' || CNAME3, NULL) ||
NVL2(CNAME4, ',' || CNAME4, NULL) ||
NVL2(CNAME5, ',' || CNAME5, NULL) ||
NVL2(CNAME6, ',' || CNAME6, NULL) ||
NVL2(CNAME7, ',' || CNAME7, NULL) ||
NVL2(CNAME8, ',' || CNAME8, NULL) COLUMNS
FROM (SELECT B.TABLE_NAME,
B.CONSTRAINT_NAME,
MAX(DECODE(POSITION, 1, COLUMN_NAME, NULL)) CNAME1,
MAX(DECODE(POSITION, 2, COLUMN_NAME, NULL)) CNAME2,
MAX(DECODE(POSITION, 3, COLUMN_NAME, NULL)) CNAME3,
MAX(DECODE(POSITION, 4, COLUMN_NAME, NULL)) CNAME4,
MAX(DECODE(POSITION, 5, COLUMN_NAME, NULL)) CNAME5,
MAX(DECODE(POSITION, 6, COLUMN_NAME, NULL)) CNAME6,
MAX(DECODE(POSITION, 7, COLUMN_NAME, NULL)) CNAME7,
MAX(DECODE(POSITION, 8, COLUMN_NAME, NULL)) CNAME8,
COUNT(*) COL_CNT
FROM (SELECT SUBSTR(TABLE_NAME, 1, 30) TABLE_NAME,
SUBSTR(CONSTRAINT_NAME, 1, 30) CONSTRAINT_NAME,
SUBSTR(COLUMN_NAME, 1, 30) COLUMN_NAME,
POSITION
FROM USER_CONS_COLUMNS) A,
USER_CONSTRAINTS B
WHERE A.CONSTRAINT_NAME = B.CONSTRAINT_NAME
AND B.CONSTRAINT_TYPE = 'R'
GROUP BY B.TABLE_NAME, B.CONSTRAINT_NAME) CONS
WHERE COL_CNT > ALL
(SELECT COUNT(*)
FROM USER_IND_COLUMNS I
WHERE I.TABLE_NAME = CONS.TABLE_NAME
AND I.COLUMN_NAME IN (CNAME1, CNAME2, CNAME3, CNAME4, CNAME5,
CNAME6, CNAME7, CNAME8)
AND I.COLUMN_POSITION <= CONS.COL_CNT
37           GROUP BY I.INDEX_NAME) ;
TABLE_NAME CONSTRAINT_NAME      COLUMNS
--------------- -------------------- ---------------
EMP_1  FK_EMP_1      DEPTNO
1 row selected.

====外键上面要建立索引===========