从子查询 mysql 中获取最大值列

Question

i have a mysql query as

SELECT date,shortcode,SUM(count) as myCount 
FROM mytable 
WHERE smsc='123' 
  AND username NOT REGEXP '[A-Za-z]+' 
  AND DATE(date) >= CURDATE() - INTERVAL 7 DAY 
GROUP BY shortcode,date 
ORDER BY date ASC

Which gives the result as following which is perfectly fine

date	shortcode	myCount
2021-02-18	123	7
2021-02-18	231	15
2021-02-19	783	117
2021-02-19	894	115
2021-02-20	009	70
2021-02-20	565	15

now what i want to do is get max value of maxcount from each day and corresponding shortcode so what i did is

Select date,Max(myCount) as maxim,shortcode 
from ( SELECT date,shortcode,SUM(count) as myCount 
       FROM mytable 
       WHERE smsc='123' 
         AND username NOT REGEXP '[A-Za-z]+' 
         AND DATE(date) >= CURDATE() - INTERVAL 7 DAY 
       GROUP BY shortcode,date 
       ORDER BY date ASC ) as a 
GROUP BY a.date;

which is not giving me the right result my desired result is

date       | shortcode | maxim
2021-02-18 | 231       |15
2021-02-19 | 783       |117
2020-02-20 | 009       |70

Answer 1

You can use common table expression and row_number() to achieve your desired result:

with cte as (
select date,shortcode,mycount,row_number()over(partition by date order by mycount desc) rn from (SELECT date,shortcode,SUM(count) as myCount 
FROM mytable 
WHERE smsc='123' 
  AND username NOT REGEXP '[A-Za-z]+' 
  AND DATE(date) >= CURDATE() - INTERVAL 7 DAY 
GROUP BY shortcode,date )t)
select date,shortcode,mycount from cte where rn=1

This query will generate a sequence for each date orderring by mycount in descendent order. So always the first row for each date will contain the max mycount.

Answer 2

If you can use a variable, the query is:

SET @x='';
SELECT
@x:=date,shortcode,myCount FROM (
  SELECT date,shortcode,SUM(count) as myCount 
  FROM mytable 
  WHERE smsc='123' 
    AND username NOT REGEXP '[A-Za-z]+' 
    AND DATE(date) >= CURDATE() - INTERVAL 7 DAY 
  GROUP BY shortcode,date 
  ORDER BY date ASC,myCount DESC
  ) a
WHERE @x<>date
;

Fiddle