Can We Change Data Type in SQL?


Larry Thompson

Can We Change Data Type in SQL?

When working with databases, it is common to encounter situations where we need to modify the data type of a column. Whether it’s due to a change in requirements or an error in the initial design, SQL provides us with the ability to alter the data type of a column. Let’s dive into how we can accomplish this.


The ALTER TABLE statement is used to modify an existing table in SQL. It allows us to add, drop, or modify columns, as well as perform other structural changes. When it comes to changing the data type of a column, we can use the ALTER TABLE statement along with the ALTER COLUMN clause.

To change the data type of a column in SQL, you need to have the necessary privileges on the table. Once you have the required permissions, you can use the following syntax:

ALTER TABLE table_name
ALTER COLUMN column_name new_data_type;


  • The table_name is the name of the table that contains the column you want to modify.
  • The column_name represents the name of the column you want to change.
  • The new_data_type specifies the desired new data type for that column.

An Example:

To illustrate how changing data types work in SQL, let’s consider a scenario where we have a table named “employees” with a “salary” column defined as an integer (INT) and we want to change it to a decimal (DECIMAL(10, 2)).

ALTER TABLE employees

This query will alter the “salary” column in the “employees” table and change its data type to DECIMAL(10, 2). The (10, 2) specifies that the column can store up to 10 digits with 2 decimal places.

Important Considerations:

While changing data types in SQL is possible, there are a few things to keep in mind:

  • Data Loss: Changing a data type may result in potential data loss. For example, if you change a column from INT to VARCHAR, any non-numeric values will be truncated or lost.
  • Data Conversion: In some cases, SQL may automatically convert the data for you.

    For example, changing an integer column to a decimal column will convert the existing values accordingly.

  • Constraints and Indexes: Changing a column’s data type may require modifications to constraints and indexes associated with that column. Make sure to review and update them accordingly.

In conclusion, changing the data type of a column in SQL is possible using the ALTER TABLE statement with the ALTER COLUMN clause. However, it’s important to consider potential data loss, automatic data conversion, and impact on constraints and indexes when making such changes. Always double-check your queries before executing them on production databases.

I hope this article has provided you with valuable insights into changing data types in SQL. Happy coding!

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