如何获取 4 个不同值的 ID（2 个键的组合）

我得到如下表

mysql> select * from tb_dts;
+----+------+------+
| Id | key1 | key2 |
+----+------+------+
|  1 |    1 |    1 |
|  2 |    1 |    1 |
|  3 |    1 |    1 |
|  4 |    2 |    1 |
|  5 |    2 |    1 |
|  6 |    2 |    1 |
|  7 |    2 |    1 |
|  8 |    1 |    2 |
|  9 |    1 |    2 |
| 10 |    1 |    2 |
| 11 |    1 |    2 |
| 12 |    1 |    2 |
| 13 |    3 |    1 |
| 14 |    3 |    1 |
| 15 |    3 |    1 |
| 16 |    3 |    1 |
| 17 |    2 |    2 |
| 18 |    2 |    2 |
| 19 |    2 |    2 |
| 20 |    2 |    3 |
| 21 |    2 |    3 |
| 22 |    2 |    3 |
| 23 |    3 |    2 |
| 24 |    3 |    2 |
| 25 |    3 |    2 |
| 26 |    3 |    2 |
+----+------+------+
26 rows in set (0.00 sec)

我采用这样的不同值，在某些应用程序分页中使用

mysql> select distinct key1,key2 from tb_dts limit 0,4;
+------+------+
| key1 | key2 |
+------+------+
|    1 |    1 |
|    1 |    2 |
|    2 |    1 |
|    2 |    2 |
+------+------+
4 rows in set (0.00 sec)

mysql> select distinct key1,key2 from tb_dts limit 4,4;
+------+------+
| key1 | key2 |
+------+------+
|    2 |    3 |
|    3 |    1 |
|    3 |    2 |
+------+------+
3 rows in set (0.00 sec)

Through group_concat我也得到了 Id，但是，我想在中使用这个 IdWHERE Field IN类似子句where somefield IN ( ..here my Ids goes...)

mysql> select key1,key2,group_concat(Id) from tb_dts group by key1,key2 limit 0,4;
+------+------+------------------+
| key1 | key2 | group_concat(Id) |
+------+------+------------------+
|    1 |    1 | 1,2,3            |
|    1 |    2 | 8,9,10,11,12     |
|    2 |    1 | 4,5,6,7          |
|    2 |    2 | 17,18,19         |
+------+------+------------------+
4 rows in set (0.00 sec)

mysql> select key1,key2,group_concat(Id) from tb_dts group by key1,key2 limit 4,4;
+------+------+------------------+
| key1 | key2 | group_concat(Id) |
+------+------+------------------+
|    2 |    3 | 20,21,22         |
|    3 |    1 | 13,14,15,16      |
|    3 |    2 | 23,24,25,26      |
+------+------+------------------+
3 rows in set (0.00 sec)

但我该如何把它放进去WHERE Fieldname IN条款？

我需要这样的东西，作为我的tb_dts包含更多内容3000万记录，以及15真实的字段，我无法使用ID BETWEEN min_id and max_id

为了处理我需要的前 4 个唯一组合值

select * from tb_dts where Id IN (1,2,3,8,9,10,11,12,4,5,6,7,17,18,19  )

为了处理接下来的 4 个唯一组合值，我需要在我的应用程序中使用 Id，所以简而言之，我希望在我的应用程序中包含下面提到的 Idwhere Field IN clause

select * from tb_dts where Id IN (20,21,22,13,14,15,16,23,24,25,26 )

这是我的表的结构

DROP TABLE IF EXISTS `tb_dts`;
CREATE TABLE `tb_dts` (
  `Id` int(11) NOT NULL AUTO_INCREMENT,
  `key1` int(11) DEFAULT '-99',
  `key2` int(11) DEFAULT '-99',
  PRIMARY KEY (`Id`),
  KEY `main` (`key1`,`key2`)
) ENGINE=MyISAM AUTO_INCREMENT=27 DEFAULT CHARSET=latin1;

LOCK TABLES `tb_dts` WRITE;
INSERT INTO `tb_dts` VALUES (1,1,1),(2,1,1),(3,1,1),(4,2,1),(5,2,1),(6,2,1),(7,2,1),(8,1,2),(9,1,2),(10,1,2),(11,1,2),(12,1,2),(13,3,1),(14,3,1),(15,3,1),(16,3,1),(17,2,2),(18,2,2),(19,2,2),(20,2,3),(21,2,3),(22,2,3),(23,3,2),(24,3,2),(25,3,2),(26,3,2);
UNLOCK TABLES;

正如您在此处看到的，它为每个不同的组合值提供第一个找到的 ID

mysql> select Id from tb_dts group by key1,key2 limit 0,4;
+----+
| Id |
+----+
|  1 |
|  8 |
|  4 |
| 17 |
+----+
4 rows in set (0.00 sec)

但我期待一切Ids符合给定的标准，这只不过是所有 ID 都低于 4 个唯一值的情况

mysql> select key1,key2 from tb_dts group by key1,key2 limit 0,4;
+------+------+
| key1 | key2 |
+------+------+
|    1 |    1 |  --- 1,2,3
|    1 |    2 |  --- 8,9,10,11,12
|    2 |    1 |  --- 4,5,6,7 
|    2 |    2 |  --- 17,18,19
+------+------+
4 rows in set (0.00 sec)

预期产出

我期望得到Id像这样group by key1,key2 limit 0,4，这样就可以在我的WHERE IN clause.

1
2
3
8
9
10
11
12
4
5
6
7
17
18
19

对于您眼前的问题，您可以使用find_in_set像这样：

select t.*
from your_table t
where exists (
    select 1 from (
        select group_concat(Id)
        from tb_dts
        group by key1, key2
        order by key1, key2   -- very important when using limit
        limit 0, 4
    ) t2 where find_in_set(t.fieldname, t2.ids) > 0
);

虽然我不确定这是否是做你正在做的事情的最佳方式。使用 group by 创建字符串然后在该字符串中搜索会太慢。

另外，您希望在 key1、key2、id 列上有一个索引。

create index idx_tb_dts on tb_dts (key1, key2, id);

可以试试这个：

select t.*
from your_table t
where exists (
    select 1
    from tb_dts t1
    inner join (
        select distinct key1, key2
        from tb_dts
        order by key1, key2
        limit 0, 4
    ) t2 on t1.key1 = t2.key1
    and t1.key2 = t2.key2
    where t1.id = t.fieldname
);

您应该了解分组依据或不同部分可能会对性能造成很大影响。如果有一个单独的表包含唯一的 key1、key2 并在它们上有唯一的索引，那就更好了。

create table the_keys_table(
    key1 int not null,
    key2 int not null,
    primary key (key1, key2)
);

然后您可以将下面的 tb_dts 替换为该表，如下所示：

select key1, key2       -- no distinct or group by needed.
from the_keys_table
order by key1, key2
limit 0, 4

您的最终查询将变为：

select t.*
from your_table t
where exists (
    select 1
    from tb_dts t2
    where (key1, key2) in (
        select key1, key2
        from the_keys_table
        order by key1, key2
        limit 0, 4
    ) and t1.id = t.fieldname
);