Which SQL statement is used to change the data type of an existing column in a table?

To change the data type of an existing column in a table, you would use the ALTER TABLE statement in SQL. Here are the steps:

1. First, you need to know the name of the table and the column that you want to change.

2. Then, you use the ALTER TABLE statement to modify the table. The syntax is as follows:

   ALTER TABLE table_name

3. After that, you use the ALTER COLUMN command to specify the column that you want to change. The syntax is as follows:

   ALTER COLUMN column_name

4. Finally, you specify the new data type for the column. The syntax is as follows:

   ALTER COLUMN column_name new_data_type;

So, the complete SQL statement would look like this:

ALTER TABLE table_name ALTER COLUMN column_name new_data_type;

Please note that not all database systems support the ALTER COLUMN command. In some databases, you might need to use the MODIFY keyword instead of ALTER COLUMN. Also, changing the data type of a column with existing data can cause data loss or corruption if the existing data doesn't fit the new data type.