SQL Alter Column type

Alter Column type in SQL is used to change or recreate the data type of existing column.

Understand with Example

The Tutorial brings you the simplest and easiest example, which helps you to understand SQL Alter Column type. The Table 'Stu_Table' is created with the help of create statement specifying its field attribute and data type. The insert into statement add the records or rows to the table. The Select statement return you the records added to the table using insert into statement.

Create Table Stu_Table

create table Stu_Table(Stu_Id varchar(2), Stu_Name varchar(10), 
Stu_Class  varchar(10))

Insert data into Stu_Table

insert into Stu_Table (Stu_Id, Stu_Name) values(1,'Komal');
insert into Stu_Table (Stu_Id, Stu_Name) values(2,'Ajay');
insert into Stu_Table (Stu_Id, Stu_Name) values(3,'Rakesh');
insert into Stu_Table (Stu_Id, Stu_Name) values(4,'Bhanu');
insert into Stu_Table (Stu_Id, Stu_Name) values(5,'Santosh');

Stu_Table

+--------+----------+-----------+
| Stu_Id | Stu_Name | Stu_Class |
+--------+----------+-----------+
| 1      | Komal    | 10        |
| 2      | Ajay     | 10        |
| 3      | Rakesh   | 10        |
| 4      | Bhanu    | 10        |
| 5      | Santosh  | 10        | 
+--------+----------+-----------+

Describe Stu_Table

The Describe Stu_Table show you the field, data type, null etc of the table 'Stu_Table'. 

+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| Stu_Id    | varchar(2)  | YES  |     |         |       |
| Stu_Name  | varchar(10) | YES  |     |         |       |
| Stu_Class | varchar(10) | YES  |     |         |       |
+-----------+-------------+------+-----+---------+-------+

Alter column type Query

The Alter Table alter the table 'stu_Table' and MODIFY keywords modify the data type of Stu_Id(varchar (2)) into Stu_Id( int(3)). 

ALTER TABLE Stu_Table MODIFY Stu_Id int(3)

Describe Stu_Table

When you see the structure of table using Describe Stu_Table, the output is displayed as:

+-----------+--------------+------+-----+---------+-------+
| Field     | Type         | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+-------+
| Stu_Id    | int(3)       | YES  |     |         |       |
| Stu_Name  | varchar(10)  | YES  |     |         |       |
| Stu_Class | varchar(10)  | YES  |     |         |       |
+-----------+--------------+------+-----+---------+-------+

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