Oracle主键约束

一 作用

确保表当中每一行数据的唯一性

二 主键特点

非空 唯一

一张表中只能设计一个主键约束

主键约束可以由多个字段构成，这种情况被称为联合主键或复合主键

三 主键约束

1、在创建表时设置主键约束

CREATE TABLE tabl_name(

column_name datatype PRIMARY_KEY,...

)

1. sql> create table userinfo_p
2. 2(id number(6,0) primary key,
3. 3 username varchar2(20),
4. 4 userpwd varchar2(20));
6. 表已创建。
8. sql> desc userinfo_p
9. 名称是否为空?类型
10. -----------------------------------------------------------------------------
11. ID NOT NULL NUMBER(6)
12. USERNAME VARCHAR2(20)
13. USERPWD VARCHAR2(20)

CONSTRAINT constraint_name

PRIMARY KEY(column_name1,...)

1. sql> create table userinfo_p1(
2. 2 id number(6,0),monospace; margin: 8px 0px;" class="language-sql">4 userpwd varchar2(20),
3. 5 constraint pk_id_username primary key(id,username));
5. 表已创建。
6. sql> desc userinfo_p1;
7. 名称是否为空?类型
8. -----------------------------------------------------------------------------
9. ID NOT NULL NUMBER(6)
10. USERNAME NOT NULL VARCHAR2(20)
11. USERPWD VARCHAR2(20)
14. sql> desc user_constraints
15. 名称是否为空?类型
16. -----------------------------------------------------------------------------
17. OWNER VARCHAR2(30)
18. CONSTRAINT_NAME NOT NULL VARCHAR2(30)
19. CONSTRAINT_TYPE VARCHAR2(1)
20. TABLE_NAME NOT NULL VARCHAR2(30)
21. SEARCH_CONDITION LONG
22. R_OWNER VARCHAR2(30)
23. R_CONSTRAINT_NAME VARCHAR2(30)
24. DELETE_RULE VARCHAR2(9)
25. STATUS VARCHAR2(8)
26. DEFERRABLE VARCHAR2(14)
27. DEFERRED VARCHAR2(9)
28. VALIDATED VARCHAR2(13)
29. GENERATED VARCHAR2(14)
30. BAD VARCHAR2(3)
31. RELY VARCHAR2(4)
32. LAST_CHANGE DATE
33. INDEX_OWNER VARCHAR2(30)
34. INDEX_NAME VARCHAR2(30)
35. INVALID VARCHAR2(7)
36. VIEW_RELATED VARCHAR2(14)
37. sql>select constraint_name from user_constraints where table_name='USERINFO_P1';
39. CONSTRAINT_NAME
40. ------------------------------
41. PK_ID_USERNAME
42. sql>select constraint_name from user_constraints where table_name='USERINFO_P';
44. CONSTRAINT_NAME
45. ------------------------------
46. SYS_C0011056

2、在修改表时添加主键约束

ADD CONSTRAINT constraint_name

PRIMARY KEY(column_name1,...);

1. sql> alter table userinfo
2. 2 add constraint pk_id primary key(id);
4. 表已更改。
5. sql> desc user_constraints
6. 名称是否为空?类型
7. -----------------------------------------------------------------------------
8. OWNER VARCHAR2(30)
9. CONSTRAINT_NAME NOT NULL VARCHAR2(30)
10. CONSTRAINT_TYPE VARCHAR2(1)
11. TABLE_NAME NOT NULL VARCHAR2(30)
12. SEARCH_CONDITION LONG
13. R_OWNER VARCHAR2(30)
14. R_CONSTRAINT_NAME VARCHAR2(30)
15. DELETE_RULE VARCHAR2(9)
16. STATUS VARCHAR2(8)
17. DEFERRABLE VARCHAR2(14)
18. DEFERRED VARCHAR2(9)
19. VALIDATED VARCHAR2(13)
20. GENERATED VARCHAR2(14)
21. BAD VARCHAR2(3)
22. RELY VARCHAR2(4)
23. LAST_CHANGE DATE
24. INDEX_OWNER VARCHAR2(30)
25. INDEX_NAME VARCHAR2(30)
26. INVALID VARCHAR2(7)
27. VIEW_RELATED VARCHAR2(14)
29. sql>select constraint_name from user_constraints where table_name='USERINFO';
30. CONSTRAINT_NAME
31. ------------------------------
32. PK_ID

3、更改约束名称

RENAME CONSTRAINT old_name

TO new_name

1. 2 rename constraint pk_id to new_pk_id;
2. sql>select constraint_name from user_constraints where table_name='USERINFO';
3. CONSTRAINT_NAME
4. ------------------------------
5. NEW_PK_ID

4、删除主键约束

disABLE|ENABLE CONSTRAINT constraint_name

1. 2 disable constraint new_pk_id;
2. sql>select constraint_name,status from user_constraints where table_name='USERINFO';
3. CONSTRAINT_NAME STATUS
4. --------------------------------------
5. NEW_PK_ID disABLED

DROP CONSTRAINT constraint_name

1. 2 drop constraint new_pk_id;
2. 未选定行

DROP PRIMARY KEY[CASCARDE]

CASCARDE用于级联删除。

1. sql> desc userinfo_p
2. USERNAME VARCHAR2(20)
3. USERPWD VARCHAR2(20)
4. sql> alter table userinfo_p
5. 2 drop primary key;
7. 表已更改。
8. ID NUMBER(6)
9. USERPWD VARCHAR2(20)