Using EXISTS within a GROUP BY clause

Question

Is it possible to do the following:
I have a table that looks like this:

declare @tran_TABLE TABLE(
EOMONTH DATE,
AccountNumber INT,
CLASSIFICATION_NAME VARCHAR(50),
Value Float

)

INSERT INTO @tran_TABLE VALUES('2018-11-30','123','cat1',10)
INSERT INTO @tran_TABLE VALUES('2018-11-30','123','cat1',15)
INSERT INTO @tran_TABLE VALUES('2018-11-30','123','cat1',5 )
INSERT INTO @tran_TABLE VALUES('2018-11-30','123','cat2',10)
INSERT INTO @tran_TABLE VALUES('2018-11-30','123','cat3',12)
INSERT INTO @tran_TABLE VALUES('2019-01-31','123','cat1',5 )
INSERT INTO @tran_TABLE VALUES('2019-01-31','123','cat2',10)
INSERT INTO @tran_TABLE VALUES('2019-01-31','123','cat2',15)
INSERT INTO @tran_TABLE VALUES('2019-01-31','123','cat3',5 )
INSERT INTO @tran_TABLE VALUES('2019-01-31','123','cat3',2 )
INSERT INTO @tran_TABLE VALUES('2019-03-31','123','cat1',15)


EOMONTH     AccountNumber   CLASSIFICATION_NAME     Value
2018-11-30  123                     cat1                10
2018-11-30  123                     cat1                15
2018-11-30  123                     cat1                5
2018-11-30  123                     cat2                10
2018-11-30  123                     cat3                12
2019-01-31  123                     cat1                5
2019-01-31  123                     cat2                10
2019-01-31  123                     cat2                15
2019-01-31  123                     cat3                5
2019-01-31  123                     cat3                2
2019-03-31  123                     cat1                15

I want to produce a result where it will check whether in each month, for each AccountNumber (just one in this case) there exists a CLASSIFICATION_NAME cat1, cat2, cat3.
If all 3 exist for the month, then return 1 but if any are missing return 0.

The result should look like:

EOMONTH     AccountNumber   CLASSIFICATION_NAME
2018-11-30    123                   1                               
2019-01-31    123                   1                       
2019-03-31    123                   0   

But I want to do it as compactly as possible, without first creating a table that groups everything by CLASSIFICATION_NAME, EOMONTH and AccountNumber and then selects from that table.
For example, in the pseudo code below, is it possible to use maybe an EXISTS statement to do the group by?

SELECT 
    EOMONTH
    ,AccountNumber
    ,CASE WHEN EXISTS (CLASSIFICATION_NAME = 'cat1' AND 'cat2' AND 'cat3') THEN 1 ELSE 0 end 
    ,SUM(Value) AS totalSpend
FROM @tran_TABLE
GROUP BY 
    EOMONTH
    ,AccountNumber

Answer 1

You could emulate this behavior by counting the distinct classifications that answer this condition (per group):

SELECT 
    EOMONTH
    ,AccountNumber
    ,CASE COUNT(DISTINCT CASE WHEN classification_name IN ('cat1', 'cat2', 'cat3') THEN classification_name END) 
          WHEN 3 THEN 1 
          ELSE 0 
     END
    ,SUM(Value) AS totalSpend
FROM @tran_TABLE
GROUP BY 
    EOMONTH
    ,AccountNumber