如何针对这种情况编写更好的SQL

Question

我有一个名为“ DEVICE ”的表，其中包含以下列：

------------------------------------------
SN | User_ID |  State    | ... 
------------------------------------------
1 |  1001   | deployed  | ...
2 |  1001   | deploying | ...
3 |  1002   | inventory | ...
4 |  1003   | deploying | ...
5 |  1001   | deploying | ...
6 |  1002   | synced    | ...
7 |  1002   | synced    | ...
8 |  1010   | synced    | ...
9 |  1008   | unsynced  | ...
---------------------------------------

如您所见，此表列出了所有设备，这些设备按其user_id属于不同的用户。 同样对于所有这些设备，它们的状态是以下5种类型之一：

"inventory", 
"deployed", 
"deploying", 
"synced"
"unsynced". 

我需要一个SQL查询，该查询返回的user_id包含每个州的最大设备数。 例如，对于第一个表中的上述数据集，返回为：

-----------------------------------------------------------
User_ID     |    State    |   Maximum 
-----------------------------------------------------------
1001        |    deployed |     1 
1001        |    deploying|     2
1002        |    inventory|     1
1002        |    synced   |     2 
1008        |    unsynced |     1 
------------------------------------------------------------

到目前为止，我创建的SQL是这样的：

SELECT 
    STATE, ACCOUNT, CNT 
from 
( select account_id as ACCOUNT, state as STATE, count(*) as CNT 
  from DEVICE group by account_id, state ) T1
where  
    ( STATE, CNT ) 
IN 
    ( select STATE, MAX(CNT) 
from 
( select account_id as ACCOUNT, state as STATE, count(*) as CNT 
   from DEVICE group by account_id, state ) T2 
Group by STATE
);

太丑了 有更好的方法吗？

谢谢，

插口

Answer 1

您可以创建一个中间摘要表或类似的视图：

drop table if exists device_summary;

create table device_summary as
    select user_id, state, count(*) as counter
    from device
    group by user_id, state;

然后，您可以像这样运行查询以获取所需的结果：

select d.*
from device_summary d
inner join (
    select state, max(counter) as maxcounter
    from device_summary
    group by state
) d1 on d.state = d1.state and d.counter = d1.maxcounter;

范例： https ： //rextester.com/ZMZH93648

Answer 2

您可以按以下方式使用ROW_NUMBER分析函数：

SELECT
    B.USER_ID,
    B.STATE,
    B.CNT
FROM
    (
        SELECT
            ROW_NUMBER() OVER(
                PARTITION BY A.STATE
                ORDER BY
                    A.CNT DESC
            ) AS RN,
            A.USER_ID,
            A.STATE,
            A.CNT
        FROM
            (
                SELECT
                    USER_ID,
                    STATE,
                    COUNT(1) CNT
                FROM
                    DEVICE
                GROUP BY
                    USER_ID,
                    STATE
            ) A
    ) B
WHERE
    B.RN = 1

db <> fiddle演示

干杯！！

Answer 3

尝试这个：

SELECT User_ID, State, count(*) AS Maximum
FROM DEVICE
GROUP BY User_ID, State
ORDER BY User_ID, State

Answer 4

您可以使用窗口函数，但只需要一个子查询级别：

SELECT USER_ID, STATE, CNT
FROM (SELECT USER_ID, STATE, COUNT(*) as CNT,
             ROW_NUMBER() OVER (PARTITION BY state ORDER BY COUNT(*) DESC) as seqnum
      FROM DEVICE
      GROUP BY USER_ID, STATE
     ) us
WHERE seqnum = 1;

注意：如果有联系，则返回任意用户。 如果要全部使用，请使用RANK()而不是ROW_NUMBER() 。

注意：窗口功能仅在版本8起的MySQL中可用。