查询以获取每种类型的最大ID

Question

I need to get max X.Id from each Specific kind, Example:

Table:

Id | Kind
---------
1  |  20
2  |  20
3  |  15
4  |  15
---------

My query needs to get the Ids 2 and 4, because my kinds are 15 and 20, this is my current query:

SELECT max(Id)
   FROM X
WHERE KIND = 15 or KIND = 20

But this query only returns id 4. I need 2 and 4, the max Id for each kind. I don't want to run more than one query. With subqueries and more than one query I know how to do.

I would like to know how to do with only one query.

Can anyone help me?

Answer 1

You need to add GROUP BY clause:

SELECT max(Id) as ID
   FROM X
WHERE KIND = 15 or KIND = 20
GROUP BY KIND

The result will be:

ID 
-----
2
4  

Suggestion

You can use IN for simplicity:

SELECT max(Id) as ID
   FROM X
WHERE KIND IN (15,20)
GROUP BY KIND

Answer 2

You have to use group by kind

Group by Clause

SELECT max(Id)
FROM X
WHERE KIND = 15 or KIND = 20
group by Kind
order by 1

SQL Fiddle

Answer 3

Create table Test (Id int, Kind int)
Insert Test(Id,Kind) Values (1, 20)
Insert Test(Id,Kind) Values (2, 20)
Insert Test(Id,Kind) Values (3, 15)
Insert Test(Id,Kind) Values (4, 15)
Insert Test(Id,Kind) Values (5, 10)
Insert Test(Id,Kind) Values (6, 10)

Select * from Test

Select MAX(Id) from Test
Where Kind in (20, 15)
Group by Kind

Select MAX(Id) from Test
Group by Kind
Having Kind in (20, 15)

Drop Table Test

Answer 4

SELECT max(Id), KIND
   FROM X
Group by KIND