SQL ALTER COLUMN Keyword

The ALTER TABLE ... ALTER COLUMN command in SQL allows you to modify the data type of an existing column within a table. This is useful when you need to change the way data is stored in a column, for example, if you initially chose an incorrect data type or if your data requirements have changed.

ALTER COLUMN: Definition and Usage

It's important to note that changing a column's data type can have implications for existing data. If the existing data doesn't fit the new data type (for instance, trying to change a text column to an integer column with text values), you might encounter errors. Always carefully consider potential data loss or conversion issues before altering a column's data type.

Syntax

ALTER TABLE table_name
ALTER COLUMN column_name new_data_type;
      

Example

Changing a Column's Data Type

This example changes the data type of the 'BirthDate' column in the 'Employees' table to 'year'. (Note: The specific data type available will depend on your database system.)

ALTER TABLE Employees
ALTER COLUMN BirthDate year;