How to perform joins on non-primary columns and complex select statements in loopback 4?

Describe the bug

Hi i am new to loopback and need to create an API with business logic that contains several complex queries. I cant seem to find a way to join two tables with non-primary columns. For example, select * from e_c left join e on e.ed=e_c.ed Table relations: e_c.ed fk to ed table on id e.ed fk to ed table on id

On the same note writing complex select statements are also needed. For example, select (case when completed_on is null then 1 else 0 end) flag from e or select sum(rating) from f_b

Kindly provide some method by which these can be achieved via loopback 4

Logs

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Additional information

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Reproduction

Non viene indicato alcun file sorgente, test o punto di ingresso. Inizia esaminando le API di relazione e query di LoopBack 4 confrontandole con gli esempi di join su colonne non primarie e di SELECT complesse; il lavoro è completato quando viene identificato un approccio supportato e documentato oppure vengono documentati chiaramente la limitazione e l'ambito richiesto.