1. mysql> show create table user\G
    2. *************************** 1. row ***************************
    3.        Table: user
    4. Create Table: CREATE TABLE `user` (
    5.   `id` int(11) DEFAULT NULL COMMENT '表的ID',
    6.   `username` varchar(20) COLLATE utf8_icelandic_ci DEFAULT NULL,
    7.   `password` varchar(20) COLLATE utf8_icelandic_ci DEFAULT NULL
    8. ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_icelandic_ci
    9. 1 row in set (0.00 sec)
    12. ## 添加user表 将ID设值为主键
    13. mysql> alter table user add  primary key (id);
    14. Query OK, 0 rows affected (0.06 sec)
    15. Query OK, 0 rows affected (0.06 sec)
    16. Records: 0  Duplicates: 0  Warnings: 0
    18. mysql> show create table user\G;
    19. *************************** 1. row ***************************
    20.        Table: user
    21. Create Table: CREATE TABLE `user` (
    22.   `id` int(11) NOT NULL COMMENT '表的ID',
    23.   `username` varchar(20) COLLATE utf8_icelandic_ci DEFAULT NULL,
    24.   `password` varchar(20) COLLATE utf8_icelandic_ci DEFAULT NULL,
    25.   PRIMARY KEY (`id`)
    26. ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_icelandic_ci
    27. 1 row in set (0.00 sec)
    29. ## 修改表 将ID设值为自动增长类型 并且为非空
    30. mysql> alter table user change id  id int not null auto_increment;
    31. Query OK, 2 rows affected (0.03 sec)
    32. Records: 2  Duplicates: 0  Warnings: 0
    34. ## 设值自增ID的起始值
    35. mysql> alter table user  auto_increment = 3;
    36. Query OK, 0 rows affected (0.01 sec)
    37. Records: 0  Duplicates: 0  Warnings: 0
    41. mysql> show create table user\G;
    42. *************************** 1. row ***************************
    43.        Table: user
    44. Create Table: CREATE TABLE `user` (
    45.   `id` int(11) NOT NULL AUTO_INCREMENT,
    46.   `username` varchar(20) COLLATE utf8_icelandic_ci DEFAULT NULL,
    47.   `password` varchar(20) COLLATE utf8_icelandic_ci DEFAULT NULL,
    48.   PRIMARY KEY (`id`)
    49. ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_icelandic_ci
    50. 1 row in set (0.00 sec)