SQL - count relation instances -


i have sql diagram:

enter image description here

i want subscribers likes 0 reports.

started by: select * subscriber having count(...)

how count how many reporters subscriber likes?

a relationship should it's own table in sql database?

i'm not sure understand last question, sounds nice time not in clause.

select * subscriber id not in (select subscriberid                  likes                      inner join reporter on reporter.id = likes.reporterid)

the inner query there finds subscriber ids have been reported, outer 1 grabs other ones. might able improve efficiency of query changing inner join in, you'd have play it.

as far task of counting them, i'd this. group , such, simple,

select *, (select count(*)            likes                inner join reporter on reporter.id = likes.reporterid            likes.subscriberid = subscriber.id) reporterscount subscriber

note listed task of finding ones 0 reporters, first query faster, because able short-circuit, rather having count every reporter every row. of course, neither should bad long you've got appropriate indexes.


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