Use `ALTER TABLE table_name ALTER COLUMN column_name TYPE new_data_type;` in PostgreSQL
Use `ALTER TABLE table_name MODIFY COLUMN column_name new_data_type;` in MySQL
Use `ALTER TABLE table_name ALTER COLUMN column_name new_data_type;` in SQL Server
Use `ALTER TABLE table_name ALTER COLUMN column_name TYPE new_data_type USING column_name::new_data_type;` in PostgreSQL when conversion is needed
Use `ALTER TABLE table_name MODIFY column_name new_data_type;` in Oracle
Back up the table before changing the datatype
Ensure existing data is compatible with the new datatype
Update constraints, indexes, and dependent objects if needed