sql - first value in group by -


i want set column in group by table based on first (actually, only) value in group.

specifically, given table

id   1    t 1    t 2    f 3    t

i want produce table

id    multiplicity  goodn 1     2             0 2     1             0 3     1             1

where goodn 1 if , if multiplicity 1 , good t:

select id, count(*) multiplicity,        if (count(*) > 1, 0, if(good = 't', 1, 0)) goodn ...

the question is: how extract first (in case, only) value of good group?

ps. there cheaper way test group has size 1 count(*)=1?

if count 1, both max(good) , min(good) "first" row in group.

select id, count(*) multiplicity,        if (count(*) > 1, 0, if(max(good) = 't', 1, 0)) goodn ...

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