PL/SQL - how to create a constraint for a tablecolumn which is already created

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how to create a constraint for a tablecolumn which is already created

Total Answers and Comments: 3

Last Update: May 03, 2008 Asked by: subbaraovangalli

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Submitted by: krishnaindia2007

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

Above answer was rated as good by the following members:
vanishavadlya

April 06, 2007 08:24:33

priya_sri

RE: how to create a constraint for a tablecolumn which...

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

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April 09, 2007 04:35:29

hindol_saha

Member Since: March 2007 Contribution: 15

RE: how to create a constraint for a tablecolumn which...

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

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May 03, 2008 05:00:06

krishnaindia2007

Member Since: September 2007 Contribution: 854

RE: how to create a constraint for a tablecolumn which is already created

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

Is this answer useful? Yes | No

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