referencing data from another table without using a join
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
briley last edited by
Since you don't need to return any data from the shipping_details table, you can use a https://en.wikipedia.org/wiki/Relational_algebra#Semijoin_(%E2%8B%89)(%E2%8B%8A) , which can be written with either
INand a subquery or
EXISTSand 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 --
from customers as c
( select 1
from shipping_details as sd
where sd.province = 'NS'
and sd.shipping_detail_id = c.shipping_detail_id -- correlation