Can I Change Data Type in SQL?


Scott Campbell

In SQL, the data type of a column determines the kind of data that can be stored in that column. But what if you need to change the data type of a column?

Can you do it? The answer is yes, you can change the data type in SQL.


The ALTER TABLE statement is used to modify an existing table in SQL. It allows you to add, modify, or delete columns, as well as change the data type of a column.

Changing Data Type

To change the data type of a column, you need to use the ALTER TABLE statement followed by the ALTER COLUMN clause. Here’s an example:

ALTER TABLE table_name
ALTER COLUMN column_name new_data_type;

Note: The syntax may vary slightly depending on the database management system you are using.


Let’s say we have a table called “employees” with a column named “age” which is currently defined as an integer. Now, we want to change its data type to smallint. Here’s how we can do it:

ALTER TABLE employees
ALTER COLUMN age smallint;

This will alter the “age” column in the “employees” table and change its data type to smallint.

Data Type Restrictions

Note: Keep in mind that not all database management systems support changing data types without restrictions. Some systems may impose certain limitations or require additional steps for altering a column’s data type.

  • Data Loss: When changing a data type, you need to be cautious about potential data loss. For example, if you change a column from a larger data type to a smaller one, you may lose data that exceeds the new size limit.
  • Constraints and Indexes: If the column you are trying to modify has any constraints or indexes associated with it, you may need to drop and recreate them after changing the data type.
  • Data Conversion: Depending on the specific database management system, there might be automatic or manual data conversion required while changing the data type.


In SQL, the ALTER TABLE statement allows you to change the data type of a column. However, it’s important to consider any restrictions imposed by your database management system and be cautious of potential data loss or required conversions. Always make sure to back up your data before making any changes to your database structure.

Now that you know how to change data types in SQL using the ALTER TABLE statement, you can confidently modify columns in your tables as needed.

I hope this tutorial was helpful! If you have any further questions or need assistance with SQL, feel free to explore our other tutorials.

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