Select from 2 tables with common key and than left join(unique result)

Question

Hi,
I have 2 tables that have a common id (Customer_id) and I have a third table which contain her key consist of 3 column ( Customer_id , rms_customer_id,billind_tree_id) and have the manager_name field
I am using a left join because not all the customers have a manager.
I need to take only the manager_name field from the left join but the problem is that I am not getting a unique name results because the customer_id is not the primary key(only part of )
so I have use the following :
left join
( select * from ACCOUNT_Manager am where
rms_customer_id <= all (select rms_customer_id from ACCOUNT_Manager am2 where
am2.customer_id = am.customer_id )) am
on c.ID = am.CUSTOMER_ID (C is one of the first 2 tables with the ID as key)
Is there anyway more efficient of doing it ?
Thanks

Answer 1

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