Mysql Alter Table Identity
Mysql Alter Table Identity is used to change the existing structure of table
and add ID column as identity key that is used to uniquely define the records in
the table.
Understand with Example
The Tutorial illustrate an example from 'Mysql Alter Table Identity'. To
understand and elaborate an example, we create a table "userform" with
required fieldnames and datatypes respectively.
Create table "userform" :
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| username | varchar(100) | YES | | | |
| fname | varchar(100) | YES | | | |
| email | varchar(100) | YES | | | |
| count | bigint(20) | YES | | 100 | | |
The Alter Table modifies the table 'userform 'and add ID as Primary Key
that uniquely identifies the records in the table.
| ALTER TABLE userform ADD ID INT NOT NULL AUTO_INCREMENT FIRST, ADD PRIMARY KEY (ID); |
After alter the table "userform"
+----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+----------------+
| ID | int(11) | NO | PRI | | auto_increment |
| username | varchar(100) | YES | | | |
| fname | varchar(100) | YES | | | |
| email | varchar(100) | YES | | | |
| count | bigint(20) | YES | | 100 | | |
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