The PRIMARYI KEY Constrainti
Defined at either the table level or the column level
SQL> CREATE TABLE |
dept( |
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deptno |
NUMBER(2), |
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dname |
VARCHAR2(14), |
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loc |
VARCHAR2(13), |
5CONSTRAINT dept_dname_uk UNIQUE (dname),
6CONSTRAINT dept_deptno_pk PRIMARY KEY(deptno));
11-12
The FOREIGNI KEY Constrainti
DEPT
PRIMARY |
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DEPTNO |
DNAME |
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LOC |
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KEY |
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-------- |
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10 |
ACCOUNTING |
NEW YORK |
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20 |
RESEARCH |
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DALLAS |
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... |
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EMP |
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FOREIGN |
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EMPNO |
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ENAME |
JOB |
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COMM |
DEPTNO |
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KEY |
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7839 |
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KING |
PRESIDENT |
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10 |
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7698 |
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BLAKE |
MANAGER |
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30 |
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Not allowed |
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Insert into |
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(DEPTNO 9 |
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does not exist |
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in the DEPT |
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7571 |
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FORD |
MANAGER |
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200 |
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9 |
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table |
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7571 |
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FORD |
MANAGER |
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200 |
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Allowed |
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11-13
The FOREIGNI KEY Constrainti
Defined at either the table level or the column level
SQL> CREATE TABLE emp(
2 |
empno |
NUMBER(4), |
3 |
ename |
VARCHAR2(10) NOT NULL, |
4 |
job |
VARCHAR2(9), |
5 |
mgr |
NUMBER(4), |
6hiredate DATE,
7 |
sal |
NUMBER(7,2), |
8 |
comm |
NUMBER(7,2), |
9 |
deptno |
NUMBER(7,2) NOT NULL, |
10 |
CONSTRAINT emp_deptno_fk FOREIGN KEY (deptno) |
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11 |
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REFERENCES dept (deptno)); |
11-14
FOREIGNI KEY Constrainti Keywords
•• FOREIGNI KEY
Definesfi thet columnl inin thet childild tablet le att thet tablet le constrainttr i t levell l
•• REFERENCES
IdentifiesI tifi thet tablet le and columnl inin thet parentr t tablet le
•• ON DELETE CASCADE
Allowsll deletionl ti inin thet parentr t tablet le and deletionl ti off thet dependentt rowsr inin thet
11-15childild tablet le
The CHECK Constrainti
•• Definesfi a conditioniti thatt t each rowr mustt satisfyti fy
•• Expressionsr i thatt t arere nott allowed:ll :
–Referencesf r toto pseudocolumnsl CURRVAL,, NEXTVAL,, LEVEL,, and ROWNUM
–Callslls toto SYSDATE,, UID,I , USER,, and USERENV functionsf ti
–Queriesri thatt t referr f r toto othert r valuesl inin othert r rowsr
..., deptno NUMBER(2),
CONSTRAINT emp_deptno_ck
CHECK (DEPTNO BETWEEN 10 AND 99),...
11-16
Addingi a Constrainti
ALTER TABLE table
ADD [CONSTRAINT constraint] type (column);
•• Add orr drop,r , butt nott modify,if , a constrainttr i t
•• Enablele orr disablei le constraintstr i ts
•• Add a NOT NULL constrainttr i t by usingi thet
MODIFYI clausel
11-17
Addingi a Constrainti
Add a FOREIGN KEY constraint to the EMP table indicating that a manager must already exist as a valid employee in the EMP table.
SQL> ALTER TABLE |
emp |
2ADD CONSTRAINT emp_mgr_fk
3 FOREIGN KEY(mgr) REFERENCES emp(empno);
Table altered.
11-18
Droppingi a Constrainti
•• Remove thet managerr constrainttr i t fromfr thet EMP tablet le..
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SQL> |
ALTER TABLE |
emp |
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2 |
DROP CONSTRAINT |
emp_mgr_fk; |
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Table altered. |
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•• Remove thet PRIMARYI KEY constrainttr i t on thet DEPT tablet le and dropr thet associatedi t FOREIGNI KEY constrainttr i t on thet EMP..DEPTNO columnl ..
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SQL> |
ALTER TABLE |
dept |
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2 |
DROP PRIMARY KEY CASCADE; |
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Table altered. |
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11-19
Disablingi li Constraintsi
•• Executete thet DISABLEI clausel off thet
ALTER TABLE statementt t t toto deactivateti te an integrityi t rity constrainttr i t..
•• Applyly thet CASCADE optionti toto disablei le dependentt integrityi t rity constraintstr i ts..
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SQL> |
ALTER TABLE |
emp |
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|
2 |
DISABLE CONSTRAINT |
emp_empno_pk CASCADE; |
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Table altered. |
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11-20
Enablingli Constraintsi
•• Activateti te an integrityi t rity constrainttr i t currentlyrr tly disabledi l inin thet tablet le definitionfi iti by usingi thet ENABLE clausel ..
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SQL> |
ALTER TABLE |
emp |
|
|
2 |
ENABLE CONSTRAINT |
emp_empno_pk; |
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Table altered. |
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•• A UNIQUEI orr PRIMARYI KEY indexi isis automaticallyt ti lly createdr t ifif you enablele a UNIQUEI key orr PRIMARYI KEY constrainttr i t..
11-21