mysql 查询每个组的 select 最大值，如果最大值大于该组的所有其他值

Question

I have a table named tab1 like this:

id	obj	col2	val
1	obj1	item1	2
2	obj2	item2	5
3	obj1	item3	4
4	obj2	item1	5
5	obj3	item4	2
6	obj3	item2	1

How to find the row with the maximum value for each object in the obj column. The maximum value of an object should be strictly greater than the other values of of the object.

The output should be like this:

id	obj	col2	val
3	obj1	item3	4
5	obj3	item4	2

SELECT id,obj,col2,max(val) 
FROM tab1
GROUP BY obj

id	obj	col2	val
3	obj1	item3	4
2	obj2	item2	5
5	obj3	item4	2

I tried this query but the output includes the obj2 whose max value isn't strictly greater than the second max value (both the max and the second max value of obj2 is 5)

Answer 1

Using DENSE_RANK as mentioned by @Rick James.

select id, obj, col2, val,cnt from (
   select *, 
   dense_rank() over (partition by obj order by val) rn,
   count(val) over (partition by obj,val) cnt,
   count(val) over (partition by obj) cnt1
   from max_tab) X
where
X.rn <> 1
AND X.cnt = 1
OR X.cnt1 = 1;

Adjust the clause x.cnt1 , as per requirements related to objects with single row.

Refer fiddle here .