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One method to alter a column definition is to use a  MODIFY  clause.  The name of the column to be  changed must be specified, followed by its new definition. Assume that the ID column's data type must be  changed from  INT to  BIGINT, to allow the table to accommodate larger identification numbers.  In  addition, the column needs to be changed to  UNSIGNED to disallow negative values. The following  statement accomplishes this task:  ALTER TABLE eu_countries MODIFY new_population BIGINT(12) NOT NULL; That ALTER TABLE statement changes the table structure as follows:  +----------------------+-------------------+-------+------+----------+--------+  | Field                    | Type                | Null  | Key  | Default | Extra |  +----------------------+-------------------+-------+------+----------+--------+  | name                   | char(52)          | NO   |         | NULL    |          |  | new_population | decimal(12,0) | NO   |         | NULL    |