ALTER TABLE table_name
ALTER COLUMN column_name new_data_type(size);
#SQL Server
ALTER TABLE Customers
ALTER COLUMN age VARCHAR(2);
#MySQL
ALTER TABLE Customers
MODIFY COLUMN age VARCHAR(2);
#Oracle
ALTER TABLE Customers
MODIFY age VARCHAR(2);
#PostgreSQL
ALTER TABLE Customers
ALTER COLUMN age TYPE VARCHAR(2);
ALTER TABLE employees
ALTER COLUMN last_name VARCHAR(75) NOT NULL;
'This adds 'NOT NULL' to excisting column counting in the table mytable'
ALTER TABLE mytable ALTER COLUMN counting INT NOT NULL;
ALTER TABLE table_name
ALTER COLUMN column_name column_type;
EXEC sp_RENAME 'table_name.oldColumn_name' , 'newColumn_name', 'COLUMN'
ALTER TABLE Customers
ALTER COLUMN age VARCHAR(2);
sp_rename 'employees.last_name', 'lname', 'COLUMN';
sp_rename 'table_name.old_column_name', 'new_column_name', 'COLUMN';
ALTER TABLE table_name
DROP COLUMN column_name;