Oracle主鍵Primary Key包含非空約束及唯一約束。

添加主鍵的語句

alter table table_nameadd constraint cons_name primary key(col_name);

查看主鍵是否被創建成功

select dbms_metadata.get_ddl(‘OBJECT_TYPE‘,‘NAME‘,‘SCHEMA‘) from dual;

OBJECT_TYPE (TABLE,PARTITION,INDEX......)

NAME (OBJECT_NAME)

SCHEMA?(INSTANCE)

對應object表中的相應內容：

select object_type,object_name,owner from dba_objects

獲取到的DDL語句中表示已經創建了主鍵列，該列位于CUSTTEL上CREATE?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"

(?"CUSTTEL"?VARCHAR2(20),

"USERLEVEL"?NUMBER(*,0)?NOT?NULL?ENABLE,

"CUSTID"?VARCHAR2(20)

)?PCTFREE?10?PCTUSED?40?INITRANS?1?MAXTRANS?255?NOCOMPRESS?LOGGING

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"?;

ALTER?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"?MODIFY?("USERLEVEL"?NOT?NULL?ENABLE);

創建主鍵后發現該表增加了唯一索引及主鍵字段CREATE?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"

(?"CUSTTEL"?VARCHAR2(20),

"USERLEVEL"?NUMBER(*,0)?NOT?NULL?ENABLE,

"CUSTID"?VARCHAR2(20),

CONSTRAINT?"PK_PRIMARY"?PRIMARY?KEY?("CUSTTEL")

USING?INDEX?PCTFREE?10?INITRANS?2?MAXTRANS?255

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"??ENABLE

)?PCTFREE?10?PCTUSED?40?INITRANS?1?MAXTRANS?255?NOCOMPRESS?LOGGING

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"?;

CREATE?UNIQUE?INDEX?"NEWCCS"."PK_PRIMARY"?ON?"NEWCCS"."USERLEVELBYTEL_BAK"?("CUSTTEL")

PCTFREE?10?INITRANS?2?MAXTRANS?255

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"?;

ALTER?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"?ADD?CONSTRAINT?"PK_PRIMARY"?PRIMARY?KEY?("CUSTTEL")

USING?INDEX?PCTFREE?10?INITRANS?2?MAXTRANS?255

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"??ENABLE;

ALTER?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"?MODIFY?("USERLEVEL"?NOT?NULL?ENABLE);

驗證：

反復向表中插入數據 insert into userlevelbytel values(‘10010‘,‘3‘,‘ ‘);

出現如下錯誤提示(唯一約束錯誤)：

ORA-00001: unique constraint (NEWCCS.PK_PRIMARY) violated

插入空值 insert into userlevelbytel values(‘‘,‘3‘,‘ ‘);

出現如下錯誤提示(唯一約束錯誤)：

ORA-01400: cannot insert NULL into ("NEWCCS"."USERLEVELBYTEL_BAK"."CUSTTEL")

單獨添加唯一約束對比區別

刪除該表主鍵：

alter table userlevelbytel_bak drop constraint pk_primary;CREATE?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"

(?"CUSTTEL"?VARCHAR2(20),

"USERLEVEL"?NUMBER(*,0)?NOT?NULL?ENABLE,

"CUSTID"?VARCHAR2(20),

CONSTRAINT?"UNIQUE_CUSTTEL"?UNIQUE?("CUSTTEL")

USING?INDEX?PCTFREE?10?INITRANS?2?MAXTRANS?255?COMPUTE?STATISTICS

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"??ENABLE

)?PCTFREE?10?PCTUSED?40?INITRANS?1?MAXTRANS?255?NOCOMPRESS?LOGGING

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"?;

CREATE?UNIQUE?INDEX?"NEWCCS"."UNIQUE_CUSTTEL"?ON?"NEWCCS"."USERLEVELBYTEL_BAK"?("CUSTTEL")

PCTFREE?10?INITRANS?2?MAXTRANS?255?COMPUTE?STATISTICS

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"?;

ALTER?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"?MODIFY?("USERLEVEL"?NOT?NULL?ENABLE);

ALTER?TABLE?"NEWCCS"."USERLEVELBYTEL_BAK"?ADD?CONSTRAINT?"UNIQUE_CUSTTEL"?UNIQUE?("CUSTTEL")

USING?INDEX?PCTFREE?10?INITRANS?2?MAXTRANS?255?COMPUTE?STATISTICS

STORAGE(INITIAL?65536?NEXT?1048576?MINEXTENTS?1?MAXEXTENTS?2147483645

PCTINCREASE?0?FREELISTS?1?FREELIST?GROUPS?1?BUFFER_POOL?DEFAULT)

TABLESPACE?"NEWCCS"??ENABLE;

可以看到唯一約束被創建

測試：

反復插入非空記錄：

ORA-00001: unique constraint (NEWCCS.UNIQUE_CUSTTEL) violated

反復插入空記錄：

select * from userlevelbytel_bak where custtel is null;

查詢結果為多個重復的空記錄

這里面可以看出唯一約束僅對非空值進行約束，而在Oracle中NULL值無法比較，因此即使反復插入，唯一約束也無法限制，但在組合約束條件下，比如(A,B,NULL)則是可以進行比較的。

舉例：

alter table userlevelbytel_bak add constraint unique_custtel unique(custtel,userlevel);

反復插入空記錄：

ORA-00001: unique constraint (NEWCCS.UNIQUE_CUSTTEL) violated

原文：http://onlinekof2001.blog.51cto.com/3106724/1582962

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