MySQL多行同一表
我有一个MySQL表,其中保存了几行配置数据,即:MySQL多行同一表,mysql,Mysql,我有一个MySQL表,其中保存了几行配置数据,即: id item value1 value2 2 class ship bow 3 class car tires 5 reg ship level1 7 reg ship level2 9 reg car level5 我试图创建一个查询,选择item='class',并返回与初始查询+item='reg'和value1=value1(来自初始结果)
id item value1 value2
2 class ship bow
3 class car tires
5 reg ship level1
7 reg ship level2
9 reg car level5
我试图创建一个查询,选择item='class',并返回与初始查询+item='reg'和value1=value1(来自初始结果)匹配的所有行的数据集
因此,在这种情况下,结果集应该如下所示:
class ship bow reg ship level1
class ship bow reg ship level2
class car tires reg car level5
我有点沮丧,希望这是有意义的。谢谢你给我指明了正确的方向 您必须将表本身连接起来。假设您的表名为
configs
(因为您没有告诉我们它的名称),类似这样的功能应该可以工作:
SELECT
t1.*,
t2.*
FROM
table t1
LEFT JOIN table t2 ON t2.item = 'reg' AND t2.value1 = t1.value1
WHERE
t1.item = 'class'
select t1.item, t1.value1, t1.value2, t2.item, t2.value1, t2.value2
from configs as t1
inner join configs as t2
on t2.value1 = t1.value1 and t2.item = 'reg'
where t1.item = 'class';
如果您需要结果中返回的所有没有匹配的行reg
行,请将internaljoin
更改为左外连接
。如果希望此查询正常执行,请确保在项
和值1上有索引
下面是一个概念的快速证明,显示了上述查询的工作原理:
mysql> create table configs (
-> id int unsigned primary key auto_increment,
-> item varchar(32) not null,
-> value1 varchar(32) not null,
-> value2 varchar(32) not null,
-> index (item),
-> index (value1)
-> ) engine=innodb charset=utf8;
Query OK, 0 rows affected (0.01 sec)
mysql> insert into configs (id, item, value1, value2) values
-> (2, 'class', 'ship', 'bow'),
-> (3, 'class', 'car', 'tires'),
-> (5, 'reg', 'ship', 'level1'),
-> (7, 'reg', 'ship', 'level2'),
-> (9, 'reg', 'car', 'level5');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from configs;
+----+-------+--------+--------+
| id | item | value1 | value2 |
+----+-------+--------+--------+
| 2 | class | ship | bow |
| 3 | class | car | tires |
| 5 | reg | ship | level1 |
| 7 | reg | ship | level2 |
| 9 | reg | car | level5 |
+----+-------+--------+--------+
5 rows in set (0.00 sec)
mysql> select t1.item, t1.value1, t1.value2, t2.item, t2.value1, t2.value2
-> from configs as t1
-> inner join configs as t2
-> on t2.value1 = t1.value1 and t2.item = 'reg'
-> where t1.item = 'class';
+-------+--------+--------+------+--------+--------+
| item | value1 | value2 | item | value1 | value2 |
+-------+--------+--------+------+--------+--------+
| class | ship | bow | reg | ship | level1 |
| class | ship | bow | reg | ship | level2 |
| class | car | tires | reg | car | level5 |
+-------+--------+--------+------+--------+--------+
3 rows in set (0.00 sec)
有时候用代码来做这些事情更容易,而不是sql@Toby艾伦:是的,但是在这种情况下SQL是非常直接的。select列应该更改以匹配问题中要求的内容。另外,table
是一个SQL保留字,因此您应该在其周围加上反勾或将其更改为其他内容。在编辑问题之前已发布了答案,为了答案的清晰性,我不会对其进行更改。对问题的唯一编辑是格式。没有进行内容编辑。可以。同意,在格式化示例结果集之前,结果集是相同的,我还没有注意到,为了说明从同一个表中选择原始结果集和其他结果集的方法,答案是足够的。我认为您有一个错误,因为您正在比较t2.value1=t1.value1,因为我认为on子句应该是value1=item。@詹姆斯布莱克:不,我说得对。再次阅读问题并查看他的样本数据。项
列仅包含值class
和reg
。value1
列是他想要匹配的内容。非常详细。我能够在很短的时间内测试和实现。谢谢