Constraint against duplication

Question

how can i make a constraint on a varchar2 column to prohibit the duplication of data in its rows , although itsnt a primary key in the table ?!

Answer 1

Hi
Yes, you can! Define a unique key on that column
Example of table creation:
-- Create table
create table TEST
  COL1 NUMBER not null,
  COL2 VARCHAR2(30)
tablespace USERS
  pctfree 10
  initrans 1
  maxtrans 255
  storage
    initial 64K
    minextents 1
    maxextents unlimited
-- Create/Recreate primary, unique and foreign key constraints
alter table TEST
  add constraint PK_TEST primary key (COL1)
  using index
  tablespace USERS
  pctfree 10
  initrans 2
  maxtrans 255
  storage
    initial 64K
    minextents 1
    maxextents unlimited
alter table TEST
  add constraint UK_TEST unique (COL2)
  using index
  tablespace USERS
  pctfree 10
  initrans 2
  maxtrans 255
  storage
    initial 64K
    minextents 1
    maxextents unlimited
  );Example:
Connected to Oracle Database 10g Express Edition Release 10.2.0.1.0
Connected as hr
SQL> desc test;
Name Type         Nullable Default Comments
COL1 NUMBER                                
COL2 VARCHAR2(30) Y                        
SQL> select * from user_constraints uc where uc.table_name = 'TEST';
OWNER                          CONSTRAINT_NAME                CONSTRAINT_TYPE TABLE_NAME                     SEARCH_CONDITION                                                                 R_OWNER                        R_CONSTRAINT_NAME              DELETE_RULE STATUS   DEFERRABLE     DEFERRED  VALIDATED     GENERATED      BAD RELY LAST_CHANGE INDEX_OWNER                    INDEX_NAME                     INVALID VIEW_RELATED
HR                             PK_TEST                        P               TEST                                                                                                                                                                                      ENABLED  NOT DEFERRABLE IMMEDIATE VALIDATED     USER NAME               15/03/2009  HR                             PK_TEST                               
HR                             UK_TEST                        U               TEST                                                                                                                                                                                      ENABLED  NOT DEFERRABLE IMMEDIATE VALIDATED     USER NAME               15/03/2009  HR                             UK_TEST                               
SQL> insert into test(col1, col2) values (1, 'john');
1 row inserted
SQL> insert into test(col1, col2) values (2, 'john');
insert into test(col1, col2) values (2, 'john')
ORA-00001: unique constraint (HR.UK_TEST) violated
SQL> Regards,