序
本文主要研究一下mysql如何用一个列来存储多个值
实例
用bit类型
-- 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 |
+---------------+------------------+
-- 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 |
+---------------+------------------+
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 |
+----+---------------+------------------+
用int/bigint类型
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 |
+-------------+
-- 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 |
+-------------+------------------+
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 |
+----+-------------+------------------+
用varchar类型
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 |
+-------------+
-- 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 |
+-------------+
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 |
+----+-------------+
用set类型
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');
-- 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 |
+-------------+
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 |
+----+-------------+
小结
mysql用单列存储多值通常用于一对多的反范式处理，具体可以用bit、int/bigint、varchar、set类型来实现，缺点是不支持索引。
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