Join questionn - Select must return only one record - sql

Question

I have 4 tables in my SQL Server 2008 database :
CONTACT
CONTACT_DETAILS
PLANS
PLANS_DETAILS
Every record is recorded in CONTACT and CONTACT_DATAILS but a CONTACT can have 0, 1, 2 or more records in PLANS, Active or Cancelled.
So I did this:
SELECT *
from CONTACT as c
left join PLANS as pp on pp.PKEY = c.PKEY
left join PLANS_DETAILS as pd on pd.PDKEY = p.PDKEY
inner join CONTACT_DETAILS as cd on cd.DKEY = c.DKEY
WHERE c.KEY = '267110' and PP.STATUS = 'Active'
"267110" have 1 active PLAN so it shows me 1 line, everything I need.
But if I put
WHERE c.KEY = '100003' and PP.STATUS = 'Active'
"100003" have 2 cancelled plans, so the result is empty. If I remove PP.STATUS = 'Active' , it returns me 2 identical results, but I need just one.
In resume: I need a select that returns me 1 row only. If there is an active plan, return the columns, if not, return the columns null. If someone have 1 cancelled and 1 active plan, return me only the active plan columns.

Answer 1

The answer to your question is to move the condition on pp to the on clause.
SELECT *
from CONTACT c inner join
CONTACT_DETAILS cd
on cd.DKEY = c.DKEY left join
PLANS pp
on pp.PKEY = c.PKEY AND PP.STATUS = 'Active' left join
PLANS_DETAILS pd
on pd.PDKEY = p.PDKEY
WHERE c.KEY = '267110' ;
In addition, when you have a series of inner and left joins, I recommend putting all the inner joins first, followed by the outer joins. That makes it clear which joins are used for keeping records and which for filtering.

Answer 2

Just add an ORDER BY PP.STATUS DESC and a TOP 1 clause, and delete the and PP.STATUS = 'Active', like this
SELECT TOP 1 * from CONTACT as c
left join PLANS as pp on pp.PKEY = c.PKEY
left join PLANS_DETAILS as pd on pd.PDKEY = p.PDKEY
inner join CONTACT_DETAILS as cd on cd.DKEY = c.DKEY
WHERE c.KEY = '100003'
ORDER BY PP.STATUS DESC

Answer 3

SELECT *
from CONTACT c
left join
(
select * from
(select
[whatever you need from this table]
,row_number over(partition by [keys in this table] order by status asc) rnk
from PLANS)
where rnk = 1
) pp
on pp.PKEY = c.PKEY
left join PLANS_DETAILS pd
on pd.PDKEY = p.PDKEY
inner join CONTACT_DETAILS cd
on cd.DKEY = c.DKEY
WHERE c.KEY = '100003'