SQL获取行等于某值的最大列数

Question

If I have Table with 3-columns:

Date | Name  | Num
oct1 | Bob   | 2
oct2 | Zayne | 1   
oct1 | Test  | 5    
oct2 | Apple | 7

I want to retrieve the rows where Num is MAX ,

WHERE Date = oct1 or Date = oct2

So I want result to be:

oct1 Test 5
oct2 Apple 7

MYSQL is preferred. But SQL answer be given also. Thanks.

Answer 1

You can try below using correlated subquery

select * from tablename a 
 where num in (select max(num) from tablename b where a.date=b.date)
 and date in ('oct1', 'oct2')

Answer 2

You can try to use correctly subquery

Schema (MySQL v5.7)

CREATE TABLE T(
   Date VARCHAR(50),
   Name  VARCHAR(50), 
  Num INT
);



INSERT INTO T VALUES ('oct1','Bob',2);
INSERT INTO T VALUES ('oct2','Zayne',1);
INSERT INTO T VALUES ('oct1','Test',5);
INSERT INTO T VALUES ('oct2','Apple',7);

---

Query #1

SELECT *
FROM T t1
WHERE Num = (SELECT MAX(Num) FROM T tt WHERE t1.Date = tt.Date)
AND 
     t1.Date in ('oct1','oct2')


| Date | Name  | Num |
| ---- | ----- | --- |
| oct1 | Test  | 5   |
| oct2 | Apple | 7   |

---

View on DB Fiddle

Answer 3

It sounds like you want this query:

SELECT t1.*
FROM yourTable t1
INNER JOIN
(
    SELECT Date, MAX(Num) AS max_num
    FROM yourTable
    WHERE Date IN ('oct1', 'oct2')
    GROUP BY Date
) t2
    ON t1.Date = t2.Date AND t1.Num = t2.max_num
WHERE t1.Date IN ('oct1', 'oct2');

By the way, you should seriously consider storing proper date data in an actual date or datetime column in MySQL. It appears you are just storing text right now, which would be hard to work with.

Answer 4

You can use corelated subquery just like below

 SELECT *
 FROM T t1
 WHERE Num = (SELECT MAX(Num) FROM T t2 WHERE t2.Date = t1.Date)

Fiddle link

Date    Name    Num
oct1    Test    5
oct2    Apple   7

Answer 5

As you where asking for a standard way to do this: All the answers given so far comply with the SQL standard. One more possible approach in standard SQL is to use a window function. This is only featured in MySQL as of version 8, however.

select date, name, num
from
(
  select date, name, num, max(num) over (partition by date) as max_num
  from mytable
) analyzed
where num = maxnum
order by date;

This only reads the table once, which can (but not necessarily does) speed up the query.