SQL Select With Multiple References to Single Table

Question

I have a SQL DB that contains multiple relational tables. There are some fields in the master table that reference another table multiple times. For example, say I have a database of salesmen who are responsible of sales for multiple states. My database has fields for State1, State2, and State3 all of which map back to a States table. I can't figure out for the life of me how to write a query to return a record with all the enumerated states. If I only needed one State field, I know I would do:

SELECT Master.Name, State.Enumeration AS 'State'
FROM MasterTable Master, StateTable State
WHERE Master.State1 = State.ID;

How can I expand this for all my State fields?

Thanks.

Answer 1

Returning a column from each of the unique joins to the states:

select m.Name, s1.Enumeration as State1, s2.Enumeration as State2, s3.Enumeration as State3
from MasterTable m
left join StateTable s1 on m.State1 = s1.ID
left join StateTable s2 on m.State2 = s2.ID
left join StateTable s3 on m.State3 = s3.ID

Returning 1 column of all the states from the 3 joins:

select m.Name, ISNULL(s1.Enumeration + ',','') 
               + ISNULL(s2.Enumeration + ',','') 
               + ISNULL(s3.Enumeration,'') as Enumeration
from MasterTable m
left join StateTable s1 on m.State1 = s1.ID
left join StateTable s2 on m.State2 = s2.ID
left join StateTable s3 on m.State3 = s3.ID

There is also column-queries...

select m.Name,
 ISNULL((select Enumeration from StateTable where ID = m.State1),'') as State1,
 ISNULL((select Enumeration from StateTable where ID = m.State2),'') as State2,
 ISNULL((select Enumeration from StateTable where ID = m.State3),'') as State3
from MasterTable m

Answer 2

You need to use table aliases in order to join multiple copies of the same table:

   SELECT m.Name, 
          s1.Enumeration AS 'State1',
          s2.Enumeration AS 'State2'
     FROM MasterTable m
LEFT JOIN StateTable s1 = s1.id = m.state1
LEFT JOIN StateTable s2 = s1.id = m.state2

An INNER JOIN requires that data is present - if not, the entire record is excluded. A LEFT JOIN is safer, like if the state1/2/3/etc allows NULLs...