板凳-------Mysql cookbook学习 （十一--------2)

11.6 扩展序列列的取值范围 2025-07-01
11.7 序列顶部数值的再使用
11.8 确保各行按照给定顺序重编号

思路
1、 创建表的空克隆
2、 使用insert into ......select 从源表自制行
3、删除源表， 并将克隆表重命名为源表表名
4、如果是巨大的MyISAM, 并含有多个索引，创建新表时不定义除了auto_increment列之外的索引，会使整个过程更高效

重新编号时解决主键冲突的示例
通过一个完整的可运行示例来演示如何安全地重新编号表中的主键，避免冲突。

示例场景
假设我们有一个用户表 users，其中主键 id 不是连续的（可能因为删除了某些行），现在需要重新编号使其连续。

1. 创建原始表并插入数据
sql
-- 创建原始表
CREATE TABLE users (
    id INT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- 插入一些数据（故意跳过某些ID）
INSERT INTO users (id, username, email) VALUES
(1, 'user1', '[email protected]'),
(3, 'user3', '[email protected]'),
(7, 'user7', '[email protected]'),
(10, 'user10', '[email protected]');
2. 方法一：创建新表并重新编号
sql
-- 创建新表结构（不包含主键约束）
CREATE TABLE users_new LIKE users;
ALTER TABLE users_new DROP PRIMARY KEY;

-- 插入数据并重新编号
INSERT INTO users_new (id, username, email, created_at)
SELECT 
    ROW_NUMBER() OVER (ORDER BY id) AS new_id,
    username,
    email,
    created_at
FROM users;

-- 删除旧表并重命名新表
DROP TABLE users;
RENAME TABLE users_new TO users;

-- 重新添加主键
ALTER TABLE users ADD PRIMARY KEY (id);

-- 验证结果
SELECT * FROM users;
3. 方法二：更高效的MyISAM表处理
如果表很大且是MyISAM引擎：

sql
-- 创建只有基本结构的新表（无索引）
CREATE TABLE users_new (
    id INT,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL,
    created_at TIMESTAMP
) ENGINE=MyISAM;

-- 插入数据并重新编号
INSERT INTO users_new (id, username, email, created_at)
SELECT 
    @row := @row + 1 AS new_id,
    username,
    email,
    created_at
FROM users, (SELECT @row := 0) r
ORDER BY id;

-- 删除旧表并重命名新表
DROP TABLE users;
RENAME TABLE users_new TO users;

-- 添加主键和索引
ALTER TABLE users ADD PRIMARY KEY (id);
ALTER TABLE users ADD INDEX (email);

-- 验证结果
SELECT * FROM users;
注意事项
外键约束：如果表有外键引用，需要先删除约束，操作后再重新添加

事务：在大表上操作时，考虑使用事务确保数据安全

备份：操作前务必备份数据

权限：确保有足够的权限执行这些操作

完整示例（包含外键处理）
sql
-- 创建有外键关系的表
CREATE TABLE departments (
    dept_id INT PRIMARY KEY,
    dept_name VARCHAR(50)
);

CREATE TABLE employees (
    emp_id INT PRIMARY KEY,
    emp_name VARCHAR(50),
    dept_id INT,
    FOREIGN KEY (dept_id) REFERENCES departments(dept_id)
);

-- 插入数据
INSERT INTO departments VALUES (1, 'HR'), (2, 'IT');
INSERT INTO employees VALUES 
    (5, 'Alice', 1),
    (8, 'Bob', 2),
    (12, 'Charlie', 1);

-- 1. 删除外键约束
ALTER TABLE employees DROP FOREIGN KEY employees_ibfk_1;

-- 2. 创建新表并重新编号
CREATE TABLE employees_new LIKE employees;
ALTER TABLE employees_new DROP PRIMARY KEY;

INSERT INTO employees_new (emp_id, emp_name, dept_id)
SELECT 
    ROW_NUMBER() OVER (ORDER BY emp_id) AS new_id,
    emp_name,
    dept_id
FROM employees;

-- 3. 替换表
DROP TABLE employees;
RENAME TABLE employees_new TO employees;

-- 4. 重新添加约束
ALTER TABLE employees ADD PRIMARY KEY (emp_id);
ALTER TABLE employees ADD CONSTRAINT fk_dept 
    FOREIGN KEY (dept_id) REFERENCES departments(dept_id);

-- 验证结果
SELECT * FROM employees;
通过以上方法，可以安全地重新编号表中的主键，即使存在外键约束也能正确处理。

更优的重新编号主键方法
确实有比创建新表更高效的方案，特别是在生产环境中处理大表时。以下是几种更优的方法：

方法一：使用临时列交换（无需重建表）
sql
-- 1. 添加临时列存储新ID
ALTER TABLE users ADD COLUMN new_id INT;

-- 2. 更新临时列为新编号
SET @row_number = 0;
UPDATE users 
SET new_id = (@row_number := @row_number + 1)
ORDER BY id;

-- 3. 删除原主键约束
ALTER TABLE users DROP PRIMARY KEY;

-- 4. 更新原ID列
UPDATE users SET id = new_id;

-- 5. 删除临时列并重建主键
ALTER TABLE users DROP COLUMN new_id;
ALTER TABLE users ADD PRIMARY KEY (id);
优点：

不需要创建新表

减少磁盘空间使用

保留所有原始表属性（触发器、权限等）

方法二：事务处理确保数据安全
sql
START TRANSACTION;

-- 禁用外键检查（如有外键约束）
SET FOREIGN_KEY_CHECKS = 0;

-- 使用临时变量重新编号
SET @new_id = 0;
UPDATE users 
SET id = (@new_id := @new_id + 1)
ORDER BY id;

-- 重置自增值
ALTER TABLE users AUTO_INCREMENT = @new_id + 1;

-- 重新启用外键检查
SET FOREIGN_KEY_CHECKS = 1;

COMMIT;
方法三：针对InnoDB的优化方案
sql
-- 1. 创建临时序列表
CREATE TEMPORARY TABLE sequence (new_id INT AUTO_INCREMENT PRIMARY KEY);

-- 2. 生成连续序号
INSERT INTO sequence ()
SELECT NULL FROM users ORDER BY id;

-- 3. 联表更新（单次操作完成）
UPDATE users u
JOIN sequence s ON 1=1
SET u.id = s.new_id
ORDER BY u.id
LIMIT (SELECT COUNT(*) FROM users);

-- 4. 清理
DROP TEMPORARY TABLE sequence;
方法四：使用存储过程（适合复杂场景）
sql
DELIMITER //
CREATE PROCEDURE renumber_ids()
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE old_id, new_id INT;
    DECLARE cur CURSOR FOR SELECT id FROM users ORDER BY id;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    
    SET new_id = 0;
    OPEN cur;
    
    read_loop: LOOP
        FETCH cur INTO old_id;
        IF done THEN
            LEAVE read_loop;
        END IF;
        
        SET new_id = new_id + 1;
        
        -- 只有当ID不同时才更新
        IF old_id != new_id THEN
            -- 处理可能的冲突
            UPDATE users SET id = -old_id WHERE id = old_id;
            UPDATE users SET id = new_id WHERE id = -old_id;
        END IF;
    END LOOP;
    
    CLOSE cur;
    
    -- 重置自增值
    SELECT MAX(id) INTO @max_id FROM users;
    SET @sql = CONCAT('ALTER TABLE users AUTO_INCREMENT = ', @max_id + 1);
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
END //
DELIMITER ;

-- 执行存储过程
CALL renumber_ids();
最佳实践建议
评估必要性：主键是否真的需要连续？业务上是否有此需求？

外键处理：

sql
-- 查找所有外键约束
SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE REFERENCED_TABLE_NAME = 'users';

-- 临时禁用外键检查
SET FOREIGN_KEY_CHECKS = 0;
-- 执行重编号操作...
SET FOREIGN_KEY_CHECKS = 1;
性能优化：

对大表操作时添加适当索引

分批处理（每次更新10000行）

在低峰期执行

原子性保障：

sql
START TRANSACTION;
-- 执行重编号操作
COMMIT;
-- 或出错时 ROLLBACK;
选择哪种方法取决于您的具体场景：

小表：方法一或方法二

大表：方法三或方法四

有复杂约束：存储过程方案

11.9 从某个特定值开始一个序列

mysql> create table tt01
    -> (id int unsigned not null auto_increment, primary key (id));
Query OK, 0 rows affected (0.11 sec)

mysql> insert into tt01 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt01 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt01 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> select id from tt01 order by id;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
+----+
3 rows in set (0.00 sec)

-- 删除表前先检查是否存在
DROP TABLE IF EXISTS table_name;
AI写代码
在上面的代码中，IF EXISTS 关键字用于判断表是否存在，如果表存在则执行删除操作，否则不会报错。一些需要注意的事项：

1. 数据备份
在删除表之前，务必进行数据备份。无论是误操作还是其他意外原因导致数据丢失，备份可以帮助恢复数据，避免信息丢失造成的损失。

2. 确认操作对象
在执行删除表操作前，要确保明确操作的是正确的表。避免误删其他重要表，确认操作对象是正确的是非常重要的。

3. 删除表前查看依赖关系
在删除表之前，要先查看该表是否被其他表或程序所依赖。如果存在外键关联或其他依赖关系，需要先解除这些关系，否则可能导致其他功能异常。

4. 谨慎使用DELETE语句
在删除表中数据时，要谨慎使用DELETE语句，确保只删除需要的数据行。同时，如果只是删除表而不需要保留表结构，建议使用DROP TABLE命令，效率更高。

5. 使用事务
在删除表操作中，可以使用事务来确保操作的一致性和完整性。如果删除表是一个重要的操作，可以结合事务来处理，避免意外中断导致数据不一致。

6. 注意权限控制
在删除表时，要注意当前用户是否具有足够的权限。确保只有授权人员才能执行删除表的操作，避免未经授权的删除操作带来安全风险。
————————————————                       
原文链接：https://blog.csdn.net/q7w8e9r4/article/details/138009452

mysql> drop table tt02;
Query OK, 0 rows affected (0.04 sec)

mysql> create table tt02
    -> (id int unsigned not null auto_increment, primary key (id))
    -> auto_increment = 100;
Query OK, 0 rows affected (0.04 sec)

mysql> insert into tt02 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt02 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt02 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> select id from tt02 order by id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+
3 rows in set (0.00 sec)

mysql> create table tt02
    -> (id int unsigned not null auto_increment, primary key (id))
    -> auto_increment = 100;
Query OK, 0 rows affected (0.04 sec)

mysql> insert into tt02 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt02 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt02 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> select id from tt02 order by id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+
3 rows in set (0.00 sec)

mysql> create table tt03
    -> (id int unsigned not null auto_increment, primary key (id))
    -> alter table tt03 auto_increment = 100;
Query OK, 0 rows affected (0.04 sec)

mysql> insert into tt03 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt03 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt03 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> select id from tt03 order by id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+
3 rows in set (0.00 sec)

mysql> CREATE TABLE tt04 (
    ->     id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    ->     PRIMARY KEY (id)
    -> ) ENGINE = InnoDB;
Query OK, 0 rows affected (0.04 sec)

mysql> insert into tt04 (id) values(99);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt04 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt04 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into tt04 (id) values(null);
Query OK, 1 row affected (0.01 sec)

mysql> delete from tt04 where id = 99;
Query OK, 1 row affected (0.01 sec)

mysql> select * from tt04 order by id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+
3 rows in set (0.00 sec)

11.10 序列化一个未序列的表

CREATE TABLE tt05 (
    name VARCHAR(50) NOT NULL,
    age INT NOT NULL,
    PRIMARY KEY (name)  -- 假设name是唯一的，设为主键
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

INSERT INTO tt05 (name, age) VALUES
('boris', 47),
('clarence', 62),
('abner', 53),
('alice', 71);

-- 1. 删除现有的主键约束（需要先删除依赖它的外键，如果有的话）
ALTER TABLE tt05 DROP PRIMARY KEY;

-- 2. 添加自增ID列并设为主键
ALTER TABLE tt05 
ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST,  -- 添加到第一列
ADD PRIMARY KEY (id);

mysql> select * from tt05;
+----+----------+-----+
| id | name     | age |
+----+----------+-----+
|  1 | abner    |  53 |
|  2 | alice    |  71 |
|  3 | boris    |  47 |
|  4 | clarence |  62 |
+----+----------+-----+
4 rows in set (0.00 sec)

方法 2：保留原主键，只添加自增ID（但不设为主键）
sql
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-- 仅添加自增ID列（作为普通列）
ALTER TABLE tt05 
ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST;
方法 3：创建新表并迁移数据
如果数据量不大，可以重建表：
sql
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下载
-- 1. 创建新表
CREATE TABLE tt05_new (
    id INT NOT NULL AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    age INT NOT NULL,
    PRIMARY KEY (id),
    UNIQUE KEY (name)  -- 保持name唯一
) ENGINE=InnoDB;

-- 2. 导入数据
INSERT INTO tt05_new (name, age) 
SELECT name, age FROM tt05;

-- 3. 删除旧表，重命名新表
DROP TABLE tt05;
RENAME TABLE tt05_new TO tt05;


+----------+-----+----+
| name     | age | id |
+----------+-----+----+
| abner    |  53 |  1 |
| alice    |  71 |  2 |
| boris    |  47 |  3 |
| clarence |  62 |  4 |
+----------+-----+----+
方法 1：重建表结构（推荐）
直接创建符合要求的表结构（适用于数据量小或新表）：
mysql> -- 1. 创建新表（id在第三列）
mysql> CREATE TABLE tt05_new (
    ->     name VARCHAR(50) NOT NULL,
    ->     age INT NOT NULL,
    ->     id INT NOT NULL AUTO_INCREMENT,
    ->     PRIMARY KEY (id),
    ->     UNIQUE KEY (name)  -- 可选：确保name唯一
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.08 sec)

mysql>
mysql> -- 2. 导入原数据（不指定id，让MySQL自动生成）
mysql> INSERT INTO tt05_new (name, age)
    -> SELECT name, age FROM tt05;
Query OK, 4 rows affected (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql>
mysql> -- 3. 替换旧表
mysql> DROP TABLE tt05;
Query OK, 0 rows affected (0.04 sec)

mysql> RENAME TABLE tt05_new TO tt05;
Query OK, 0 rows affected (0.04 sec)

mysql> select * from tt05;
+----------+-----+----+
| name     | age | id |
+----------+-----+----+
| abner    |  53 |  1 |
| alice    |  71 |  2 |
| boris    |  47 |  3 |
| clarence |  62 |  4 |
+----------+-----+----+
4 rows in set (0.00 sec)________________________________________
方法 2：通过 ALTER TABLE 调整（复杂）
如果必须保留原表，可通过临时列实现：
sql
复制
下载
-- 1. 移除id的自增属性（需先删除主键）
ALTER TABLE tt05 MODIFY id INT NOT NULL;
ALTER TABLE tt05 DROP PRIMARY KEY;

-- 2. 将id列重命名为临时列
ALTER TABLE tt05 CHANGE id temp_id INT;

-- 3. 在末尾添加新的自增id列
ALTER TABLE tt05 ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST;
ALTER TABLE tt05 ADD PRIMARY KEY (id);

-- 4. 将数据从temp_id复制到新id列（如果需要保留原id值）
UPDATE tt05 SET id = temp_id;

-- 5. 删除临时列
ALTER TABLE tt05 DROP COLUMN temp_id;

-- 6. 将id列移动到第三位（MySQL不支持直接移动列，需重建表）
-- 此处需使用方法1的步骤

mysql> -- 1. 删除现有id列
mysql> ALTER TABLE tt05 DROP COLUMN id;
Query OK, 4 rows affected (0.13 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> -- 2. 添加新的自增id列
mysql> ALTER TABLE tt05
    -> ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST,
    -> ADD PRIMARY KEY (id),
    -> AUTO_INCREMENT = 100;
Query OK, 0 rows affected (0.12 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from tt05;
+-----+----------+-----+
| id  | name     | age |
+-----+----------+-----+
| 100 | abner    |  53 |
| 101 | alice    |  71 |
| 102 | boris    |  47 |
| 103 | clarence |  62 |
+-----+----------+-----+
4 rows in set (0.00 sec)

11.11 使用auto_increment栏来创建多重序列

需要将自增列id单独设为主键。原表定义中同时使用name和id作为复合主键，且id为自增列，这违反了 MySQL 的规则。以下是修正后的 SQL 语句：

sql
CREATE TABLE bug (
    id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    name VARCHAR(30) NOT NULL,
    date DATE NOT NULL,
    origin VARCHAR(30) NOT NULL,
    PRIMARY KEY (id),  -- 仅使用id作为主键
    UNIQUE KEY (name)  -- 如果需要确保name唯一，可添加唯一索引
);

INSERT INTO bug (name, date, origin) VALUES
('mosquito', '2006-10-08', 'bathroom'),
('spider', '2006-10-08', 'basement'),
('fly', '2006-10-08', 'kitchen'),
('moth', '2006-10-09', 'bedroom'),
('centipede', '2006-10-09', 'garage'),
('millipede', '2006-10-09', 'back yard'),
('roach', '2006-10-09', 'kitchen'),
('bee', '2006-10-10', 'garden'),
('wasp', '2006-10-10', 'porch'),
('ladybug', '2006-10-10', 'front yard'),
('butterfly', '2006-10-11', 'garden'),
('grasshopper', '2006-10-11', 'back yard'),
('termite', '2006-10-11', 'basement'),
('flea', '2006-10-12', 'living room'),
('tick', '2006-10-12', 'front yard'),
('silverfish', '2006-10-12', 'bathroom'),
('earwig', '2006-10-13', 'garage'),
('gnat', '2006-10-13', 'kitchen'),
('firefly', '2006-10-13', 'back yard'),
('dragonfly', '2006-10-14', 'garden'),
('aphid', '2006-10-14', 'front yard'),
('caterpillar', '2006-10-14', 'garden'),
('weevil', '2006-10-15', 'pantry'),
('carpenter ant', '2006-10-15', 'basement'),
('black widow', '2006-10-15', 'garage'),
('brown recluse', '2006-10-16', 'basement'),
('cricket', '2006-10-16', 'living room'),
('housefly', '2006-10-16', 'kitchen'),
('fruit fly', '2006-10-17', 'kitchen'),
('woodlouse', '2006-10-17', 'back yard');

mysql> select * from bug order by name, id;
+----+---------------+------------+-------------+
| id | name          | date       | origin      |
+----+---------------+------------+-------------+
| 21 | aphid         | 2006-10-14 | front yard  |
|  8 | bee           | 2006-10-10 | garden      |
| 25 | black widow   | 2006-10-15 | garage      |
| 26 | brown recluse | 2006-10-16 | basement    |
| 11 | butterfly     | 2006-10-11 | garden      |
| 24 | carpenter ant | 2006-10-15 | basement    |
| 22 | caterpillar   | 2006-10-14 | garden      |
|  5 | centipede     | 2006-10-09 | garage      |
| 27 | cricket       | 2006-10-16 | living room |
| 20 | dragonfly     | 2006-10-14 | garden      |
| 17 | earwig        | 2006-10-13 | garage      |
| 19 | firefly       | 2006-10-13 | back yard   |
| 14 | flea          | 2006-10-12 | living room |
|  3 | fly           | 2006-10-08 | kitchen     |
| 29 | fruit fly     | 2006-10-17 | kitchen     |
| 18 | gnat          | 2006-10-13 | kitchen     |
| 12 | grasshopper   | 2006-10-11 | back yard   |
| 28 | housefly      | 2006-10-16 | kitchen     |
| 10 | ladybug       | 2006-10-10 | front yard  |
|  6 | millipede     | 2006-10-09 | back yard   |
|  1 | mosquito      | 2006-10-08 | bathroom    |
|  4 | moth          | 2006-10-09 | bedroom     |
|  7 | roach         | 2006-10-09 | kitchen     |
| 16 | silverfish    | 2006-10-12 | bathroom    |
|  2 | spider        | 2006-10-08 | basement    |
| 13 | termite       | 2006-10-11 | basement    |
| 15 | tick          | 2006-10-12 | front yard  |
|  9 | wasp          | 2006-10-10 | porch       |
| 23 | weevil        | 2006-10-15 | pantry      |
| 30 | woodlouse     | 2006-10-17 | back yard   |
+----+---------------+------------+-------------+
30 rows in set (0.00 sec)

mysql> select * from housewares;
+------------+------------------+
| id         | description      |
+------------+------------------+
| DIN40672US | dining table     |
| KIT00372UK | garbage disposal |
| KIT01729JP | microwave oven   |
| BED00038SG | bedside lamp     |
| BTH00485US | shower stall     |
| BTH00415JP | lavatory         |
+------------+------------------+
6 rows in set (0.00 sec)

关键修改点：
1.	将自增列serial单独设为主键（MySQL 要求自增列必须是主键）
2.	添加唯一索引UNIQUE (category, country, serial)来满足原复合主键的业务逻辑
3.	保留id列的唯一性约束

ALTER TABLE housewares
ADD category VARCHAR(3) NOT NULL FIRST,
ADD serial INT UNSIGNED NOT NULL AUTO_INCREMENT AFTER category,
ADD country VARCHAR(2) NOT NULL AFTER serial,
ADD PRIMARY KEY (serial), -- 将自增列单独设为主键
ADD UNIQUE KEY (category, country, serial), -- 添加唯一约束确保业务逻辑
ADD UNIQUE KEY (id); -- 保持原id唯一性

mysql> select * from housewares;
+----------+--------+---------+------------+------------------+
| category | serial | country | id         | description      |
+----------+--------+---------+------------+------------------+
|          |      1 |         | DIN40672US | dining table     |
|          |      2 |         | KIT00372UK | garbage disposal |
|          |      3 |         | KIT01729JP | microwave oven   |
|          |      4 |         | BED00038SG | bedside lamp     |
|          |      5 |         | BTH00485US | shower stall     |
|          |      6 |         | BTH00415JP | lavatory         |
+----------+--------+---------+------------+------------------+
6 rows in set (0.00 sec)

mysql> update housewares set category = left(id, 3);
Query OK, 6 rows affected (0.01 sec)
Rows matched: 6  Changed: 6  Warnings: 0

mysql> update housewares set serial = mid(id, 4, 5);
Query OK, 6 rows affected (0.01 sec)
Rows matched: 6  Changed: 6  Warnings: 0

mysql> update housewares set country = right(id, 2);
Query OK, 6 rows affected (0.01 sec)
Rows matched: 6  Changed: 6  Warnings: 0

mysql> alter table housewares drop id;
Query OK, 0 rows affected (0.15 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from housewares;
+----------+--------+---------+------------------+
| category | serial | country | description      |
+----------+--------+---------+------------------+
| BED      |     38 | SG      | bedside lamp     |
| KIT      |    372 | UK      | garbage disposal |
| BTH      |    415 | JP      | lavatory         |
| BTH      |    485 | US      | shower stall     |
| KIT      |   1729 | JP      | microwave oven   |
| DIN      |  40672 | US      | dining table     |
+----------+--------+---------+------------------+
6 rows in set (0.00 sec)

mysql> select category, serial, country,
    -> concat(category, lpad(serial, 5, '0'), country) as id
    -> from housewares order by category, country, serial;
+----------+--------+---------+------------+
| category | serial | country | id         |
+----------+--------+---------+------------+
| BED      |     38 | SG      | BED00038SG |
| BTH      |    415 | JP      | BTH00415JP |
| BTH      |    485 | US      | BTH00485US |
| DIN      |  40672 | US      | DIN40672US |
| KIT      |   1729 | JP      | KIT01729JP |
| KIT      |    372 | UK      | KIT00372UK |
+----------+--------+---------+------------+
6 rows in set (0.00 sec)

mysql> alter table housewares
    -> modify serial int(5) unsigned zerofill not null auto_increment;
Query OK, 0 rows affected, 2 warnings (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 2

mysql> select category, serial, country,
    -> concat(category, serial, country) as id
    -> from housewares order by category, country, serial;
+----------+--------+---------+------------+
| category | serial | country | id         |
+----------+--------+---------+------------+
| BED      |  00038 | SG      | BED00038SG |
| BTH      |  00415 | JP      | BTH00415JP |
| BTH      |  00485 | US      | BTH00485US |
| DIN      |  40672 | US      | DIN40672US |
| KIT      |  01729 | JP      | KIT01729JP |
| KIT      |  00372 | UK      | KIT00372UK |
+----------+--------+---------+------------+
6 rows in set (0.00 sec)

mysql> CREATE FUNCTION houseware_id( category varchar(3),
    ->                          serial int unsigned,
    ->                          country varchar(2))
    -> returns varchar(10) deterministic
    -> return concat(category, lpad(serial, 5, '0'), country);
Query OK, 0 rows affected (0.01 sec)

mysql> select category, serial, country,
    -> houseware_id(category, serial, country) as id
    -> from housewares;
+----------+--------+---------+------------+
| category | serial | country | id         |
+----------+--------+---------+------------+
| BED      |  00038 | SG      | BED00038SG |
| BTH      |  00415 | JP      | BTH00415JP |
| BTH      |  00485 | US      | BTH00485US |
| DIN      |  40672 | US      | DIN40672US |
| KIT      |  01729 | JP      | KIT01729JP |
| KIT      |  00372 | UK      | KIT00372UK |
+----------+--------+---------+------------+
6 rows in set (0.00 sec)