unique constraint in sql

Unique Constraint::

================

-Restricted Duplicates values but accepting nulls into a column

column level::

============

>create table test1(sno int unique,name varchar2(10) unique);

EX::

SQL> create table test1(eid int unique,ename varchar2(10) unique);

Table created.

SQL> insert into test1 values(10,'virat');

1 row created.

SQL> select * from test1;

EID ENAME

---------- ----------

10 virat

SQL> insert into test1 values(10,'rohit');

insert into test1 values(10,'rohit')

ERROR at line 1:

ORA-00001: unique constraint (SYSTEM.SYS_C007643) violated

SQL> insert into test1 values(20,'virat');

insert into test1 values(20,'virat')

ERROR at line 1:

ORA-00001: unique constraint (SYSTEM.SYS_C007644) violated

SQL> insert into test1 values(20,'rohit');

1 row created.

SQL> select * from test1;

EID ENAME

---------- ----------

10 virat

20 rohit

SQL> insert into test1(null,'raja');

insert into test1(null,'raja')

ERROR at line 1:

ORA-00928: missing SELECT keyword

SQL> insert into test1 values(null,'raja');

1 row created.

SQL> select * from test1;

EID ENAME

---------- ----------

10 virat

20 rohit

raja

SQL> insert into test1 values(null,null);

1 row created.

SQL> select * from test1;

EID ENAME

---------- ----------

10 virat

20 rohit

raja

SQL> insert into test1 values(30,null);

1 row created.

SQL> select * from test1;

EID ENAME

---------- ----------

10 virat

20 rohit

raja

table level::

===========

>create table test1(sno int,name varchar2(10),unique(sno,name));

EX::

SQL> create table test2(eid int,ename varchar2(10),unique(eid,ename));

Table created.

SQL> insert into test2 values(1,'randy');

1 row created.

SQL> select * from test2;

EID ENAME

---------- ----------

1 randy

SQL> insert into test2 values(1,'dan');

1 row created.

SQL> select * from test2;

EID ENAME

---------- ----------

1 randy

1 dan

SQL> insert into test2 values(1,'dan');

insert into test2 values(1,'dan')

ERROR at line 1:

ORA-00001: unique constraint (SYSTEM.SYS_C007645) violated

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