Primary key in oracle
In Oracle, a primary key is a single field or combination of fields. A primary key in a relational database is unique. None of the fields that are part of the primary key can contain a null value. There is only one primary key in a table.
A primary key cannot contain more than 32 columns.
A primary key can be defined in either a create table statement or alter table statement.
Create table statement using Primary key
You can create a primary key in a create table statement.
Syntax:
Create table table_name
(
Column 1 datatype(),
Column 2 datatype(),
. .
. .
. .
Column n datatype()
Constraint constraint_name primary key(column 1, column 2…..column n)
);
Commit;
Example
Look at an example, we can create a primary key in create table statement.
Create table customer
(
Customer_id number(20),
Customer_name varchar2(15),
Customer_address varchar2(100),
Customer_mob number(10),
Constraint pk_customer_id primary key (customer_id)
);
Commit;
Drop Primary key You can drop a primary key using the alter table statement.
Syntax:
Drop a primary key using alter table statement.
alter table table_name
Drop constraint constraint_name;
Example
Alter table customer
Drop constraint pk_customer_id;
Commit;
Disable Primary Key
You can disable the primary key using alter table statement.
Syntax:
Disable a primary key using alter table statement.
Alter table table_name
Disable constraint constraint_name;
Example
Alter table customer
Disable constraint pk_customer_id;
Commit;
Enable a primary key
You can enable a primary key usin an alter table statement.
Syntax:
Alter table table_name
Enable constraint constraint_name;
Example
Alter table customer
Enable constraint pk_customer_id;
Commit;
