Create & Drop a Unique Constraint - SQL Query

i) How to create a unique constraint on table student?

The following query will create a unique constraint while creating a table student on column Stud_ID.

CREATE TABLE Students
(
  Stud_ID INT  not null,
  Stud_Name varchar2(50) not null
CONSTRAINT Stud_unique UNIQUE (stud_ID)
);


The above query will create a UNIQUE constraint on the field Stud_ID.

ii) CREATE A UNIQUE constraint using ALTER TABLE statement.

Consider the table 'Students' which is already created so the following query will create a UNIQUE constraint on column Stud_ID.

ALTER TABLE Students
ADD CONSTRAINT Students_unique UNIQUE (Stud_ID);


iii) How to drop a Unique constraint?

The following query will delete a UNIQUE constraint crated on Stud_ID from table Students.

ALTER TABLE Students
DROP CONSTRAINT Students_unique;

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