使用group by函数mysql查找模式而不是MAX/AVG

我使用了下面的查询，但在测试时发现

模式

比考虑

MAX

的结果更好

SELECT MAX(rssi) AS rssii,beacon,receiver  
FROM readings 
WHERE created_datetime BETWEEN  '2018-11-29 09:46:10'  AND  '2018-11-29 10:58:50'
GROUP BY beacon,receiver;

我能够得到RSSI的模式，而只选择特定的列，我的意思是没有任何分组

SELECT rssi,count(*) as occurs
FROM readings
GROUP BY `rssi` order by occurs desc
LIMIT 1;

但我发现很难对每个小组都这样做

预期结果格式

+-------+-----------+-----------+
| rssii | beacon    |   receiver|
+-------+-----------+-----------+
|   -42 |       AAA |       XXX |
|   -49 |       AAA |       YYY |
|   -49 |       AAA |       ZZZ |
|   -44 |       BBB |       XXX |
|   -54 |       BBB |       YYY |
|   -52 |       BBB |       ZZZ |
|   -49 |       CCC |       XXX |
|   -42 |       CCC |       YYY |
|   -57 |       CCC |       ZZZ |
+-------+---------+-------------+

---

任何人都可以帮助……

您可以先获得每个信标/接收器对的

rssi

值的计数，如下所示来解决您的问题：

SELECT beacon, receiver, rssi, COUNT(*) as occurs
FROM readings
GROUP BY beacon, receiver, rssi

然后，要查找每个信标/接收器对的模式，您可以将其用作子查询，将其连接到最大

发生值的列表中

值：

SELECT beacon, receiver, rssi, occurs 
FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
      FROM readings
      GROUP BY beacon, receiver, rssi) r1
JOIN (SELECT beacon, receiver, rssi, MAX(occurs)
      FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
            FROM readings
            GROUP BY beacon, receiver, rssi) r2
      GROUP BY beacon, receiver, rssi) r3
  ON r3.beacon = r1.beacon AND r3.receiver = r1.receiver AND r3.rssi = r1.rssi

请注意，如果一个信标/接收器对有多个模式值，则将提供所有模式值。您可能希望在初始选择中使用

MAX（rssi）

，并

GROUP BY beacon，receiver

将结果限制为每对一个

rssi

值，即

SELECT beacon, receiver, MAX(rssi), occurs 
FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
      FROM readings
      GROUP BY beacon, receiver, rssi) r1
JOIN (SELECT beacon, receiver, rssi, MAX(occurs)
      FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
            FROM readings
            GROUP BY beacon, receiver, rssi) r2
      GROUP BY beacon, receiver, rssi) r3
  ON r3.beacon = r1.beacon AND r3.receiver = r1.receiver AND r3.rssi = r1.rssi
GROUP BY beacon, receiver

---

您可以通过以下方式首先获得每个信标/接收机对的

rssi

值的计数来解决问题：

SELECT beacon, receiver, rssi, COUNT(*) as occurs
FROM readings
GROUP BY beacon, receiver, rssi

然后，要查找每个信标/接收器对的模式，您可以将其用作子查询，将其连接到最大

发生值的列表中

值：

SELECT beacon, receiver, rssi, occurs 
FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
      FROM readings
      GROUP BY beacon, receiver, rssi) r1
JOIN (SELECT beacon, receiver, rssi, MAX(occurs)
      FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
            FROM readings
            GROUP BY beacon, receiver, rssi) r2
      GROUP BY beacon, receiver, rssi) r3
  ON r3.beacon = r1.beacon AND r3.receiver = r1.receiver AND r3.rssi = r1.rssi

请注意，如果一个信标/接收器对有多个模式值，则将提供所有模式值。您可能希望在初始选择中使用

MAX（rssi）

，并

GROUP BY beacon，receiver

将结果限制为每对一个

rssi

值，即

SELECT beacon, receiver, MAX(rssi), occurs 
FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
      FROM readings
      GROUP BY beacon, receiver, rssi) r1
JOIN (SELECT beacon, receiver, rssi, MAX(occurs)
      FROM (SELECT beacon, receiver, rssi, COUNT(*) as occurs
            FROM readings
            GROUP BY beacon, receiver, rssi) r2
      GROUP BY beacon, receiver, rssi) r3
  ON r3.beacon = r1.beacon AND r3.receiver = r1.receiver AND r3.rssi = r1.rssi
GROUP BY beacon, receiver

---

就像在许多其他复杂问题中一样，动态规划可以方便地解决这个问题，也很容易理解

首先在Mysql中声明两个临时变量

set @mc1 = '', @rc1 = '';

然后将它们用作临时占位符并遍历结果集

select rssi,cr, mc,rc, @mc1:=mc,@rc1:=rc from (
SELECT rssi, count(rssi) cr,beacon AS mc,receiver AS rc
FROM readings
WHERE created_datetime BETWEEN  '2018-11-29 09:46:10'  AND  '2018-11-29 10:58:50'
GROUP BY readings.beacon ,readings.receiver, rssi order by mc,rc,cr desc
) p where (mc != @mc1 or rc != @rc1)

我得到了我想要的

+------+-----+-----+-----+----------+----------+
| rssi | cr  | mc  | rc  | @mc1:=mc | @rc1:=rc |
+------+-----+-----+-----+----------+----------+
|  -53 | 127 | AAA | XXX    | AAA   | XXX |
|  -55 | 109 | AAA | YYYY   | AAA   | YYYY |
|  -52 | 194 | AAA | ZZZ    | AAA   | ZZZ |
|  -53 | 112 | BBB | XXX    | BBB   | XXX |
|  -48 | 218 | BBB | YYYY   | BBB   | YYYY |
|  -64 |  72 | BBB | ZZZ    | BBB   | ZZZ |
|  -47 | 151 | CCC| XXX     | CCC   | XXX |
|  -38 | 204 | CCC| YYYY    | CCC   | YYYY |
|  -53 | 120 | CCC| ZZZ     | CCC   | ZZZ |
|  -54 | 152 | DDD| XXX     | DDD   | XXX |
|  -62 |  80 | DDD| YYYY    | DDD   | YYYY |
|  -56 | 138 | DDD| ZZZ     | DDD   | ZZZ |
+------+-----+-----------+----------+

---

就像在许多其他复杂问题中一样，动态规划可以方便地解决这个问题，也很容易理解

首先在Mysql中声明两个临时变量

set @mc1 = '', @rc1 = '';

然后将它们用作临时占位符并遍历结果集

select rssi,cr, mc,rc, @mc1:=mc,@rc1:=rc from (
SELECT rssi, count(rssi) cr,beacon AS mc,receiver AS rc
FROM readings
WHERE created_datetime BETWEEN  '2018-11-29 09:46:10'  AND  '2018-11-29 10:58:50'
GROUP BY readings.beacon ,readings.receiver, rssi order by mc,rc,cr desc
) p where (mc != @mc1 or rc != @rc1)

我得到了我想要的

+------+-----+-----+-----+----------+----------+
| rssi | cr  | mc  | rc  | @mc1:=mc | @rc1:=rc |
+------+-----+-----+-----+----------+----------+
|  -53 | 127 | AAA | XXX    | AAA   | XXX |
|  -55 | 109 | AAA | YYYY   | AAA   | YYYY |
|  -52 | 194 | AAA | ZZZ    | AAA   | ZZZ |
|  -53 | 112 | BBB | XXX    | BBB   | XXX |
|  -48 | 218 | BBB | YYYY   | BBB   | YYYY |
|  -64 |  72 | BBB | ZZZ    | BBB   | ZZZ |
|  -47 | 151 | CCC| XXX     | CCC   | XXX |
|  -38 | 204 | CCC| YYYY    | CCC   | YYYY |
|  -53 | 120 | CCC| ZZZ     | CCC   | ZZZ |
|  -54 | 152 | DDD| XXX     | DDD   | XXX |
|  -62 |  80 | DDD| YYYY    | DDD   | YYYY |
|  -56 | 138 | DDD| ZZZ     | DDD   | ZZZ |
+------+-----+-----------+----------+

---

您预期的输出是什么？可能与您使用的MySQL版本重复？在MySQL 8.0.2和above@Madhurmysql 5.7。Madhur u共享的链接更简单，我的意思是我的问题有点不同，cse我必须找到每组信标的模式，Receiver请看：您的预期输出是什么？可能与您使用的MySQL版本重复？在MySQL 8.0.2和above@Madhurmysql 5.7。Madhur你分享的链接更简单，我的意思是我的问题有点不同，因为我必须找到每组信标的模式，receiverSee：这回答了你的问题吗？如果没有，你能提供更多的信息来帮助回答这个问题吗？否则，请考虑标注答案接受。看，这回答了你的问题吗？如果没有，你能提供更多的信息来帮助回答这个问题吗？否则，请考虑标注答案接受。看看这个，我现在可以轻松解决我的其他问题了。谢谢有了这个，我现在可以轻松地解决我的其他问题。谢谢