Redefine i to be NOT NULL, then try again
mysql>
mysql> CREATE TABLE mytbl
-> (
-> i INT,
-> c CHAR(1)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql>
mysql> ALTER TABLE mytbl MODIFY i INT NOT NULL;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE mytbl ADD PRIMARY KEY (i);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql>
mysql> drop table mytbl;
Query OK, 0 rows affected (0.00 sec)
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