join - MySql Get records only from child table where the parent key has multiple values -

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i have 2 tables parent , child. parent has field called unique_id , child has field called parent_unique_id , foreign key in child table. parent table has 4 records same unique_id , child table has 5 records same unique_id.

when join them records, getting total of 20 records each 5 records of child table repeating 4 times.

the query using 

select c.* child c join parent p on c.parent_unique_id = p.unique_id

i tried left join still getting 20 records repeated.

one method use in or exists:

select c.* child c  c.parent_unique_id in (select p.unique_id parent p);

of course, slap select distinct on query. however, requires , unnecessary processing.


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