priya_sri

• Apr 6th, 2007

 

Hi,You can create constraints using Alter commandAlter table add constraint column

hindol_saha

 Profile Answers by hindol_saha Questions by hindol_saha

• Apr 9th, 2007

 

ALTER TABLE STUDENT  ADD CONSTRAINT PK_STD_ID PRIMARY KEY (STUDENT_ID);

krishnaindia2007

 Profile Answers by krishnaindia2007 

• May 3rd, 2008

 

To add  primary key or unique key constraint

Alter table tablename add constraint constraintname  primary key / unique (column name)

To add check constraint
Alter table tablename add constraint constraintname  check (codition)


To add not null constraint
Alter table tablename modify (columnname not null)

To add  foreign key constraint
Alter table tablename add constraint constraintname foreign key(columnname) references referencedtablename(referenced columnname)

Note- We can not add primary key or not null constraint on  a column that contains null values.
We can not add unique key or primary key constraint on a column that constains duplicate vlaues