MySQL - Join & Count rows from another table

Question

I have 3 tables, like:
parent(id, name)
children(id, data, parent_id, timestamp)
table_votes(id, user_id, child_id)

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Answer 1

i am not sure if i am understanding your question correctly but to me it seems like you want to count the number of children in the tables_votes not in children. try the following:

select id, data, parent_id, timestamp, child_id
from table_votes join children on children_id.id = table_vote.child_id
where child_id = (select count(child_id) from table_vote)
and parent_id = '20'