Talk about MySQL's single-column multi-value storage

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    sequence

    This article mainly studies how mysql uses a column to store multiple values

    example

    use bit type

    • Table building and data preparation

       -- 这里定义了bit(3)，表示有3位，第一位1，第二位2，第三位4
create table t_bit_demo(
 id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
 multi_value bit(3) not null default 0
);

-- 这里插入了1，2，4的组合值
insert into t_bit_demo(multi_value) values(b'000');
insert into t_bit_demo(multi_value) values(b'001');
insert into t_bit_demo(multi_value) values(b'010');
insert into t_bit_demo(multi_value) values(b'011');
insert into t_bit_demo(multi_value) values(b'100');
insert into t_bit_demo(multi_value) values(b'101');
insert into t_bit_demo(multi_value) values(b'110');
insert into t_bit_demo(multi_value) values(b'111');

-- 这里直接插入int值也可以，比如5相当于101
-- insert into t_bit_demo(multi_value) values(5);

SELECT multi_value+0, BIN(multi_value) FROM t_bit_demo;
+---------------+------------------+
| multi_value+0 | BIN(multi_value) |
+---------------+------------------+
| 0             | 0                |
| 1             | 1                |
| 2             | 10               |
| 3             | 11               |
| 4             | 100              |
| 5             | 101              |
| 6             | 110              |
| 7             | 111              |
+---------------+------------------+

    • Bit operation query

       -- 查询第二位有值的数据
select multi_value+0,BIN(multi_value) from t_bit_demo where multi_value & 2
+---------------+------------------+
| multi_value+0 | BIN(multi_value) |
+---------------+------------------+
| 2             | 10               |
| 3             | 11               |
| 6             | 110              |
| 7             | 111              |
+---------------+------------------+

-- 查询第三位有值的数据
select multi_value+0,BIN(multi_value) from t_bit_demo where multi_value & 4
+---------------+------------------+
| multi_value+0 | BIN(multi_value) |
+---------------+------------------+
| 4             | 100              |
| 5             | 101              |
| 6             | 110              |
| 7             | 111              |
+---------------+------------------+

-- 查询只有第三位有值的数据
select multi_value+0,BIN(multi_value) from t_bit_demo where multi_value = 4
select multi_value+0,BIN(multi_value) from t_bit_demo where multi_value = 4
+---------------+------------------+
| multi_value+0 | BIN(multi_value) |
+---------------+------------------+
| 4             | 100              |
+---------------+------------------+

    • renew

       select id,multi_value+0,BIN(multi_value) from t_bit_demo
+----+---------------+------------------+
| id | multi_value+0 | BIN(multi_value) |
+----+---------------+------------------+
| 1  | 0             | 0                |
| 2  | 1             | 1                |
| 3  | 2             | 10               |
| 4  | 3             | 11               |
| 5  | 4             | 100              |
| 6  | 5             | 101              |
| 7  | 6             | 110              |
| 8  | 7             | 111              |
+----+---------------+------------------+

-- 将id为7的值移除第二个枚举
update t_bit_demo set multi_value = b'100' where id=7
select id,multi_value+0,BIN(multi_value) from t_bit_demo where id=7
+----+---------------+------------------+
| id | multi_value+0 | BIN(multi_value) |
+----+---------------+------------------+
| 7  | 4             | 100              |
+----+---------------+------------------+

    Use int/bigint types

    • Table building and data preparation

       create table t_bigint_demo(
 id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
 multi_value bigint not null default 0
);

-- 假设这里定义了1，2，4三个枚举值
insert into t_bigint_demo(multi_value) values(0);
insert into t_bigint_demo(multi_value) values(1);
insert into t_bigint_demo(multi_value) values(2);
insert into t_bigint_demo(multi_value) values(3);
insert into t_bigint_demo(multi_value) values(4);
insert into t_bigint_demo(multi_value) values(5);
insert into t_bigint_demo(multi_value) values(6);
insert into t_bigint_demo(multi_value) values(7);

select multi_value from t_bigint_demo
+-------------+
| multi_value |
+-------------+
| 0           |
| 1           |
| 2           |
| 3           |
| 4           |
| 5           |
| 6           |
| 7           |
+-------------+

    • Inquire

       -- 查询包含第二个枚举的数据
select multi_value,BIN(multi_value) from t_bigint_demo where multi_value & 2
+-------------+------------------+
| multi_value | BIN(multi_value) |
+-------------+------------------+
| 2           | 10               |
| 3           | 11               |
| 6           | 110              |
| 7           | 111              |
+-------------+------------------+

-- 查询包含第三个枚举的数据
select multi_value,BIN(multi_value) from t_bigint_demo where multi_value & 4
+-------------+------------------+
| multi_value | BIN(multi_value) |
+-------------+------------------+
| 4           | 100              |
| 5           | 101              |
| 6           | 110              |
| 7           | 111              |
+-------------+------------------+

-- 查询值为第三个枚举的数据
select multi_value,BIN(multi_value) from t_bigint_demo where multi_value =4
+-------------+------------------+
| multi_value | BIN(multi_value) |
+-------------+------------------+
| 4           | 100              |
+-------------+------------------+

    • renew

       select id,multi_value,BIN(multi_value) from t_bigint_demo
+----+-------------+------------------+
| id | multi_value | BIN(multi_value) |
+----+-------------+------------------+
| 1  | 0           | 0                |
| 2  | 1           | 1                |
| 3  | 2           | 10               |
| 4  | 3           | 11               |
| 5  | 4           | 100              |
| 6  | 5           | 101              |
| 7  | 6           | 110              |
| 8  | 7           | 111              |
+----+-------------+------------------+

-- 将id为7的值移除第二个枚举
update t_bigint_demo set multi_value = b'100' where id=7
select id,multi_value,BIN(multi_value) from t_bigint_demo where id=7
+----+-------------+------------------+
| id | multi_value | BIN(multi_value) |
+----+-------------+------------------+
| 7  | 4           | 100              |
+----+-------------+------------------+

    Use varchar type

    • Table building and data preparation

       create table t_varchar_demo(
 id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
 multi_value varchar(255) not null default ''
);

-- 假设这里定义了1，2，4三个枚举值
insert into t_varchar_demo(multi_value) values('1');
insert into t_varchar_demo(multi_value) values('2');
insert into t_varchar_demo(multi_value) values('1,2');
insert into t_varchar_demo(multi_value) values('4');
insert into t_varchar_demo(multi_value) values('1,4');
insert into t_varchar_demo(multi_value) values('2,4');
insert into t_varchar_demo(multi_value) values('1,2,4');

select multi_value from t_varchar_demo
+-------------+
| multi_value |
+-------------+
| 1           |
| 2           |
| 1,2         |
| 4           |
| 1,4         |
| 2,4         |
| 1,2,4       |
+-------------+

    • Inquire

       -- 查询包含第二个枚举的数据
select multi_value from t_varchar_demo where find_in_set('2',multi_value)
+-------------+
| multi_value |
+-------------+
| 2           |
| 1,2         |
| 2,4         |
| 1,2,4       |
+-------------+

-- 查询包含第三个枚举的数据
select multi_value from t_varchar_demo where find_in_set('4',multi_value)
+-------------+
| multi_value |
+-------------+
| 4           |
| 1,4         |
| 2,4         |
| 1,2,4       |
+-------------+

-- 查询只有第三个枚举的数据
select multi_value from t_varchar_demo where multi_value = '4'
+-------------+
| multi_value |
+-------------+
| 4           |
+-------------+

    • renew

       select * from t_varchar_demo
+----+-------------+
| id | multi_value |
+----+-------------+
| 1  | 1           |
| 2  | 2           |
| 3  | 1,2         |
| 4  | 4           |
| 5  | 1,4         |
| 6  | 2,4         |
| 7  | 1,2,4       |
+----+-------------+

-- 将id为7的值移除第二个枚举
update t_varchar_demo set multi_value = '1,4' where id=7
select * from t_varchar_demo where id=7
+----+-------------+
| id | multi_value |
+----+-------------+
| 7  | 1,4         |
+----+-------------+

    use set type

    • Table building and data preparation

       create table t_set_demo(
 id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
 multi_value set('1','2','4') not null default ''
);

insert into t_set_demo(multi_value) values('');
insert into t_set_demo(multi_value) values('1');
insert into t_set_demo(multi_value) values('2');
insert into t_set_demo(multi_value) values('1,2');
insert into t_set_demo(multi_value) values('4');
insert into t_set_demo(multi_value) values('1,4');
insert into t_set_demo(multi_value) values('2,4');
insert into t_set_demo(multi_value) values('1,2,4');

    • Inquire

       -- 查询包含第二个枚举的数据，可以用位运算也可以用find_in_set
select multi_value from t_set_demo where multi_value&2
select multi_value from t_set_demo where find_in_set('2',multi_value)
+-------------+
| multi_value |
+-------------+
| 2           |
| 1,2         |
| 2,4         |
| 1,2,4       |
+-------------+

-- 查询包含第三个枚举的数据，可以用位运算也可以用find_in_set
select multi_value from t_set_demo where multi_value&4
select multi_value from t_set_demo where find_in_set('4',multi_value)
+-------------+
| multi_value |
+-------------+
| 4           |
| 1,4         |
| 2,4         |
| 1,2,4       |
+-------------+

-- 查询值为第三个枚举的数据
select multi_value from t_set_demo where multi_value='4'
+-------------+
| multi_value |
+-------------+
| 4           |
+-------------+

    • renew

       select * from t_set_demo
+----+-------------+
| id | multi_value |
+----+-------------+
| 1  |             |
| 2  | 1           |
| 3  | 2           |
| 4  | 1,2         |
| 5  | 4           |
| 6  | 1,4         |
| 7  | 2,4         |
| 8  | 1,2,4       |
+----+-------------+

-- 将id为7的值移除第二个枚举
update t_set_demo set multi_value = '1,4' where id=7
select * from t_set_demo where id=7
select * from t_set_demo where id=7
+----+-------------+
| id | multi_value |
+----+-------------+
| 7  | 1,4         |
+----+-------------+

    summary

    MySQL uses a single column to store multiple values, which is usually used for one-to-many anti-paradigm processing. Specifically, it can be implemented with bit, int/bigint, varchar, and set types. The disadvantage is that it does not support indexes.

    doc

    mysql
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