mysql - Fetch records of parent table depending on count of children -


i have 2 tables, a , b, b has foreign keys a (i.e. a can have 0 or many children in b whereas each b record belongs 1 a record).

now want fetch records a the number of children in b lower x (including zero).

how can achieve comparison of aggregate function?

select a.*, count(b.id) child_cnt     left join b          on a.id = b.foreign_id group a.id

however, cannot add where condition child_cnt of course. pointers how desired result can achieved?

you can use having filter result

select a.*, ifnull(count(b.id), 0) child_cnt left join b on a.id = b.foreign_id group a.id having count(b.id) < x

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