MODIFY COLUMN

mysql> CREATE TABLE t1 (id int not null primary key AUTO_INCREMENT, col1 INT);
Query OK, 0 rows affected (0.11 sec)

mysql> INSERT INTO t1 (col1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE t1 MODIFY col1 BIGINT;
Query OK, 0 rows affected (0.09 sec)

mysql> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `col1` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin AUTO_INCREMENT=30001
1 row in set (0.00 sec)

mysql> ALTER TABLE t1 MODIFY col1 INT;
ERROR 1105 (HY000): unsupported modify column length 11 is less than origin 20
mysql> ALTER TABLE t1 MODIFY col1 BLOB;
ERROR 1105 (HY000): unsupported modify column type 252 not match origin 8
mysql> ALTER TABLE t1 MODIFY col1 BIGINT, MODIFY id BIGINT NOT NULL;
ERROR 1105 (HY000): can't run multi schema change