Mysql Alter Constraint
A constraint is a property in SQL assigned to a column or the set of columns
in a table that prevents certain types of inconsistent data values from being
placed in the column of the table. Constraints in SQL are used to enforce
the data integrity. This ensures the accuracy and reliability of the data in the
database.
Understand with Example
The Tutorial illustrate an example from 'Mysql Alter Constraint'. To
understand the example we simply 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 | | |
Alter column ID using the below Query:
The Alter Table is used to modify the table 'userform' and add ID as a
Primary Key constraint.
| 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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