mysql - 无法向该列添加主键/唯一键/自动增量

Question

ALTER TABLE `clinic1`.`patients` 
CHANGE COLUMN `Patient_Id` `Patient_Id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '' ,
ADD UNIQUE INDEX `Patient_Id_UNIQUE` (`Patient_Id` ASC)  COMMENT '';

ERROR 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'COMMENT ''' at line 3

SQL语句:

ALTER TABLE `clinic1`.`patients` 
CHANGE COLUMN `Patient_Id` `Patient_Id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '' ,
ADD UNIQUE INDEX `Patient_Id_UNIQUE` (`Patient_Id` ASC)  COMMENT ''

无法向该列添加主键/唯一键/自动增量

分别尝试过其中每一个

不工作

Answer 1

首先将主键删除到现有列

ALTER TABLE clinic1 MODIFY Patient_Id int(10), drop primary key;

然后修改现有列或新列以使其成为主键

ALTER TABLE test MODIFY Patient_Id int(10) unsigned NOT NULL PRIMARY KEY AUTO_INCREMENT comment '', 
ADD UNIQUE INDEX `Patient_Id_UNIQUE` (`Patient_Id` ASC)  COMMENT '';