Select sum with input from grouped query - mysql

Question

I need to make a query that selects a grouped collection of rows from a table based on user input conditions, and then in the select i will sum data from a subset of the rows.
The setup is rather expansive to describe in a post, so here is a demostration of the problem in the simplest way i can make it:
We have this table: DemoTable
ID
StaticKey
GroupKey
Value
1
A
A
2
2
A
A
2
3
A
B
2
4
A
B
2
5
A
C
2
6
A
C
2
I make a select and groups on "StaticKey".
What i would then like to do, is to, in the select clause, to select the sum of a subset of the values from the groupped data:
select
DT.GroupKey,
(select sum(D.Value) from DemoTable D where D.ID in (DT.ID) and D.GroupKey = 'A') as 'Sum of A''s',
(select COUNT(D.ID) from DemoTable D where D.ID in (DT.ID) and D.GroupKey = 'A') as 'Count of A''s'
from DemoTable DT
group by DT.StaticKey;
I hoped that the sum would result in a sum of 4 and a count of 2, but i get 2 and 1. So the input to the "select sum" seems to be just one id and not the collected ids.
GroupKey
Sum of A's
Count of A's
A
2
1
If i add a group_concat of DT.ID i get them comma separated - but is it posible to get them as a collection i can use as input to the selects?
Heres sql to create the table and queries:
CREATE TABLE DemoTable
(
ID INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
GroupKey varchar(200) null default null,
StaticKey varchar(200) not null default 'A',
Value varchar(200) null default null,
PRIMARY KEY (ID)
) ENGINE = InnoDB
DEFAULT CHARSET = utf8;
insert into DemoTable (GroupKey, Value) values ('A', 2);
insert into DemoTable (GroupKey, Value) values ('A', 2);
insert into DemoTable (GroupKey, Value) values ('B', 2);
insert into DemoTable (GroupKey, Value) values ('B', 2);
insert into DemoTable (GroupKey, Value) values ('C', 2);
insert into DemoTable (GroupKey, Value) values ('C', 2);
select DT.GroupKey,
(select sum(D.Value) from DemoTable D where D.ID in (DT.ID) and D.GroupKey = 'A') as 'Sum of A''s',
(select COUNT(D.ID) from DemoTable D where D.ID in (DT.ID) and D.GroupKey = 'A') as 'Count of A''s'
from DemoTable DT
group by DT.StaticKey;
DROP TABLE DemoTable;

Answer 1

More simple:
select GroupKey,
sum(Value) as sum_of_A,
sum(GroupKey='A') as count_of_A
from DemoTable
where GroupKey='A'
group by GroupKey;
https://dbfiddle.uk/sdYlTw57

Answer 2

Isn't it always D.ID in (DT.ID)?
select
DT.GroupKey,
(select sum(D.Value) from DemoTable D where D.GroupKey = 'A') as 'Sum of A''s',
(select COUNT(D.ID) from DemoTable D where D.GroupKey = 'A') as 'Count of A''s'
from DemoTable DT
group by DT.StaticKey;
It does the job but perhaps it's too simple...

Answer 3

You can also try this.
SELECT DT.GroupKey,
SUM(DT.Value) AS 'Sum of A''s',
COUNT(DT.ID) AS 'Count of A''s'
FROM DemoTable DT
WHERE DT.GroupKey = 'A'
GROUP BY DT.StaticKey;