Chave única no Oracle com exemplos

O que é chave única

1. Pode haver mais de uma chave única por tabela
2. Pode ser definido em uma ou mais colunas
3. As colunas que compõem a chave exclusiva podem ser nulas

Como criar a chave exclusiva

Criação de Tabela

SQL> CREATE TABLE DEPT_MASTER (
     dept_nr NUMBER UNIQUE,
     dept_name varchar2(100) NOT NULL,
     dept_status NUMBER(1,0) NOT NULL,
     created_at date
     );
 Table created.

 SQL> column  CONSTRAINT_NAME format a20
 SQL> column TABLE_NAME  format a20
 SQL> column INDEX_NAME format a20
 SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,TABLE_NAME,
   INDEX_NAME   from  user_Constraints where 
   TABLE_NAME='DEPT_MASTER';

SQL> CREATE TABLE DEPT_MASTER (
     dept_nr NUMBER ,
     dept_name varchar2(100) NOT NULL,
     dept_status NUMBER(1,0) NOT NULL,
     created_at date,
     Unique(dept_nr) );
 Table created.

 SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,TABLE_NAME,
     INDEX_NAME from  user_Constraints where 
     TABLE_NAME='DEPT_MASTER';

SQL>  CREATE TABLE DEPT_MASTER (
      dept_nr NUMBER ,
      dept_name varchar2(100) NOT NULL,
      dept_status NUMBER(1,0) NOT NULL,
      created_at date,
      constraint DEPT_UK Unique(dept_nr)      
       ); 
 Table created.

 SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,TABLE_NAME,
    INDEX_NAME    from  user_Constraints 
     where      TABLE_NAME='DEPT_MASTER';

CREATE TABLE CUSTOMER_DETAIL
(
CUSTOMER_ID   NUMBER(6,0),  
NAME VARCHAR (20)     NOT NULL,
AGE  NUMBER(6,0)      NOT NULL,
ADDRESS   VARCHAR2(25), 
SALARY   NUMBER(6,0),     
UNIQUE(CUSTOMER_ID, NAME)
);
Table Created.

SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,
    TABLE_NAME,INDEX_NAME from  user_Constraints where 
    TABLE_NAME='CUSTOMER_DETAIL';

SQL> CREATE TABLE CUSTOMER_DETAIL(
     CUSTOMER_ID   NUMBER(6,0),
     NAME VARCHAR (20)     NOT NULL,
     AGE  NUMBER(6,0)    NOT NULL,
     ADDRESS   VARCHAR2(25),
     SALARY   NUMBER(6,0),
    constraint  CUSTOMER_UK UNIQUE(CUSTOMER_ID, NAME)
     );
   
 Table created.

 SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,
     TABLE_NAME,INDEX_NAME from  user_Constraints where      TABLE_NAME='CUSTOMER_DETAIL';

Alterar tabela adicionar chave exclusiva

SQL> CREATE TABLE CUSTOMER_DETAIL(
    CUSTOMER_ID   NUMBER(6,0),
    NAME VARCHAR (20)     NOT NULL,
    AGE  NUMBER(6,0)    NOT NULL,
    ADDRESS   VARCHAR2(25),
    SALARY   NUMBER(6,0)
     ); 
 Table created.

 SQL>  select CONSTRAINT_NAME,CONSTRAINT_TYPE,
     TABLE_NAME,INDEX_NAME from  user_Constraints where    TABLE_NAME='CUSTOMER_DETAIL';

 SQL> alter table customer_detail add constraint 
      customer_uk UNIQUE(CUSTOMER_ID, NAME);
 Table altered.

 SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,TABLE_NAME,INDEX_NAME from  user_Constraints where TABLE_NAME='CUSTOMER_DETAIL';

Chave primária e chave única

SQL>  CREATE TABLE DEPT_MASTER (
      dept_nr NUMBER PRIMARY KEY,
      dept_name varchar2(100) UNIQUE,
      dept_status NUMBER(1,0) NOT NULL,
      created_at date  
      );
 Table created.

 SQL> select CONSTRAINT_NAME,CONSTRAINT_TYPE,
     TABLE_NAME,INDEX_NAME  from  
      user_Constraints where   TABLE_NAME='DEPT_MASTER';

Como encontrar a coluna associada à chave exclusiva

SQL>  CREATE TABLE DEPT_MASTER (
      dept_nr NUMBER PRIMARY KEY,
      dept_name varchar2(100) UNIQUE,
      dept_status NUMBER(1,0) NOT NULL,
      created_at date
       );
 Table created.

 SQL> select CONSTRAINT_NAME,
     CONSTRAINT_TYPE,TABLE_NAME,INDEX_NAME 
     from  user_Constraints where TABLE_NAME='DEPT_MASTER'; 

 SQL> SELECT Constraint_name, Table_name, Column_name FROM User_cons_columns where CONSTRAINT_NAME ='SYS_C00540915';  
 CONSTRAINT_NAME      TABLE_NAME     COLUMN_NAME
 -------------------- -----------   ------------
 SYS_C00540915        DEPT_MASTER   DEPT_NAME

 SQL> SELECT Constraint_name, Table_name, Column_name
     FROM User_cons_columns where CONSTRAINT_NAME ='SYS_C00540914'; 
 CONSTRAINT_NAME      TABLE_NAME           COLUMN_NAME
 -------------         ---------            ---------
 SYS_C00540914        DEPT_MASTER          DEPT_NR
 SQL> SELECT Constraint_name, Table_name, Column_name
     FROM User_cons_columns where CONSTRAINT_NAME ='SYS_C00540918';
 CONSTRAINT_NAME      TABLE_NAME           COLUMN_NAME
 -------------        ----------          ------------
 SYS_C00540918        CUSTOMER_DETAIL      CUSTOMER_ID
 SYS_C00540918        CUSTOMER_DETAIL      NAME 

Como ativar e desativar a restrição de chave exclusiva

SQL>  alter table customer_detail disable UNIQUE(CUSTOMER_ID, NAME);
 Table altered.
 SQL> alter table customer_detail disable constraint  CUST_UK;
 Table altered.
 SQL> alter table customer_detail enable  UNIQUE(CUSTOMER_ID, NAME);
 Table altered.
 SQL>  alter table customer_detail enable constraint  CUST_UK;
 Table altered.

Como eliminar a restrição Unique

SQL> alter table customer_detail drop  UNIQUE(CUSTOMER_ID, NAME);
 Table altered.
 OR
 SQL> alter table customer_detail drop constraint  CUST_UK;
 Table altered.