SQL Query to Relational Algebra -

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i have query:

select distinct a.aanbieding_id aankoop  2 <= (select count(*) aankoop a.aanbieding_id = aankoop.aanbieding_id)  order aanbieding_id

and wanne make relational algebra scheme of query, solution is: 

πid(f(count)(aanbieding_id)>=2(aankoop))

but i'm pretty sure wrong, can me please


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