All we need is an easy explanation of the problem, so here it is.
Hi all so I have a homework assignment that I am having difficulty understanding. the problem I have been given is this:
ix. Referring to the customers and shipping_details tables on the ER, display all data from the customers table but only where the province on the shipping_details table is equal to NS. Do not use a join for this requirement.
So I can complete the question easily enough using a join but I am having difficulty understanding how one can reference another table without using a join. I am trying to use a vector aggregate function but I am very unclear on how to reference a table and a value within a column of that table without using a join
How to solve :
I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.
Since you don’t need to return any data from the shipping_details table, you can use a semi-join, which can be written with either
IN and a subquery or
EXISTS and a correlated subquery.
-- Using IN -- select c.* from customers as c where c.shipping_detail_id IN ( select sd.shipping_detail_id from shipping_details as sd where sd.province = 'NS' ) ; -- Using EXISTS -- select c.* from customers as c where EXISTS ( select 1 from shipping_details as sd where sd.province = 'NS' and sd.shipping_detail_id = c.shipping_detail_id -- correlation ) ;
Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂