Mysql Alter Table Primary Key
Mysql Alter Table Primary Key is used to remove the primary key from the
table and add primary key to the existing other column of table.
Understand with Example
The Tutorial illustrate an example from 'Mysql Alter Table Primary
Key'. To understand this example, we create a table employees with required
field name and data type respectively. The createtable employee create a
table employee with Empid as primary key.
Query to create table:
CREATE TABLE `employees` (
->Empid int(10),
->Empname varchar(60),
->date date
->PRIMARY KEY(Empid)
->);
|
Query to insert data into Table named employees:
The Query insert into add
the records or rows to the table 'employee'.
mysql>insert into employees values(01,'Girish','2008-12-22');
Query OK, 1 row affected (0.02 sec)
mysql>insert into employee1 values(02,'Komal','2008-12-23');
Query OK, 1 row affected (0.02 sec)
|
Query to view data of Table named employees:
To view the detail from table 'employee' we use select
query that return the detail of table 'employees'.
mysql> select * from employee;
|
Output:
+-------+---------+------------+
| Empid | Empname | date |
+-------+---------+------------+
| 1 | Girish | 2008-12-22 |
| 2 | Komal | 2008-12-23 |
+-------+---------+------------+
2 rows in set (0.00 sec)
|
Query to view datatype of Table named employees:
The describe employees return
the Fieldname, data type, Null, Key, Default.
mysql> describe employees;
|
Output:
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| Empid | int(10) | NO | PRI | 0 | |
| Empname | varchar(60) | YES | | NULL | |
| date | date | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
|
Query for altering the Primary key of the table employees:
The Query alter is
used to change the table ' Employees' and
drop primary remove
the 'Empid' as primary key. The table is no longer to contain a primary
key.
Step1:-Drop the primary key
mysql> alter table Employees
-> drop primary key;
Query OK, 2 rows affected (0.11 sec)
Records: 2 Duplicates: 0 Warnings: 0
|
Query to view changes occurs in the datatype of Table named
employees:
mysql> describe employees;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| Empid | int(10) | NO | | 0 | |
| Empname | varchar(60) | YES | | NULL | |
| date | date | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
|
Step1:-Define the primary key
Query for defining the Primary key of the table employees:
The Query alter redefine the table Employees and add keyword insert
the 'Empname' as Primary Key in the table 'employees.
mysql> alter table employees
-> add primary key (Empname);
Query OK, 2 rows affected (0.14 sec)
Records: 2 Duplicates: 0 Warnings: 0
|
Query to view datatype of Table named employees:
mysql> describe employees;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| Empid | int(10) | NO | | 0 | |
| Empname | varchar(60) | NO | PRI | | |
| date | date | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
|
|
Del.icio.us
Digg
Google
Spurl
Blink
Furl
Simpy
Y! MyWeb
