Question

I have a table like the following:

ID                Output
-------------------------
01ABC1            AB
01ABC2            AB
01ABC3            AB
02ABC1            AC
02ABC2            AC
02ABC3            AB

I have to count the number of sets of ID’s that has the same first two digits and the output is consistent.
For example in this case
01ABC1,01ABC2 and 01ABC3 has the same output but 02ABC1,02ABC2 and 02ABC3 does not.
So the answer will be 1 set.

The output should be

ID                Count(ID)
---------------------------    
01ABC            1
02ABC            0

Answer 1

If by consistent you mean all the outputs are the same for a given set of ids that share the same first 2 digits, then this query will do the work:

select count(*) from (
    select count(distinct output) aCount from t
    group by left(id, 2)
    having aCount = 1
) final

PS: You’ve edited your question. This answers answer your second edit… the one with this expected result:

The output should be
    Count(ID)
    1