Mysql add primary key
Mysql add Primary Key is used to add primary key on the column of existing table.
Understand with Example
The section of this tutorial illustrate an example from 'Mysql Add
Primary Key'. To understand and grasp this example we create a table
'employees' with required fieldname and datatype.
Query to create table:
CREATE TABLE `employees` (
->Empid int(10),
->Empname varchar(60),
->date date
->);
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Query to insert data into Table named employees:
Once your table employees is created .The insert into keyword add the records or rows into table 'employees'.
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 'employees' we use select query that return the detail of records.
mysql> select * from employees; |
Output:-
+-------+---------+------------+ | Empid | Empname | date | +-------+---------+------------+ | 1 | Girish | 2008-12-22 | | 2 | Komal | 2008-12-23 | +-------+---------+------------+ 2 rows in set (0.00 sec) |
Query to view data type of Table named employees:
The describe employees return the table attribute like fieldname,Type,Null,Key,Default,Extra etc.
mysql> describe employees; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | Empid | int(10) | NO | | 0 | | | Empname | varchar(60) | NO | | | | | date | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+ 3 rows in set (0.00 sec) |
Query to add primary key into the Table named employees:
The Query Alter is used to redefine the table 'employees' and add keyword is used to add primary key on column 'empid'.
mysql> alter table employees
-> add primary key (empid);
Query OK, 2 rows affected (0.16 sec)
Records: 2 Duplicates: 0 Warnings: 0
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data type of Table named employees after adding primary key:
mysql> describe employees; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | Empid | int(10) | NO | PRI | 0 | | | Empname | varchar(60) | NO | | | | | date | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+ 3 rows in set (0.01 sec) |