SQL join multiple tables with/without data - sql

Question

I have no idea how to create an SQL statement to join 4 tables.
1) The 'Vendor Table will always match entries from each table on Vendor #
2) Each of the remaining 3 will match to each other by Vendor # & Seq #
3) Any combination of the 3 can have data (or not)
4) I don't want to select from the Vendor table unless I get a hit on at least one of the 3
VENDOR
Vendor # Name
-------- ----
1 Tom Smith
2 Bruce Lee
3 Seamus O’Leary
4 Jonathan Stewart
5 Benjamin Franklin
Month Range Selected
Vendor # Seq # MonthFrom MonthTo
-------- ----- --------- -------
1 1 3 6
1 2 7 9
3 2 5 6
Week Selected
Vendor # Seq # Week #
-------- ----- ------
1 1 3
3 1 4
4 1 1
Day Selected
Vendor # Seq # Day #
1 1 15
1 2 25
2 1 12
4 1 05
5 1 19
Desired Table (Joined)
Vendor# Name Seq# MonthFrom MonthTo Week# Day#
1 Tom Smith 1 3 6 3 15
1 Tom Smith 2 7 9 NULL 25
2 Bruce Lee 1 NULL NULL NULL 12
3 Seamus O’Leary 1 NULL NULL 4 NULL
3 Seamus O’Leary 2 5 6 NULL NULL
4 Jonathan Stewart 1 NULL NULL 1 05
5 Benjamin Franklin 1 NULL NULL NULL 19
The trick being that any of the 3 (not including 'Vendor') can or cannot have data and I only want a row returned if there is something from one or more of the 3.
Any Advice?

Answer 1

To join it on Vendor and Seq, we first need to have all possible combinations. Then we can filter the tables based on these combinations. I've ran the following in SQL server:
Setup
declare #Vendors table(id int, name varchar(20));
declare #MonthRangeSelected table (vendor int, seq int null, monthFrom int null, monthTo int null);
declare #WeekSelected table (vendor int, seq int null, week int null);
declare #DaySelected table (vendor int, seq int null, day int null);
insert into #Vendors
select 1, 'Tom Smith'
union all
select 2, 'Bruce Lee'
union all
select 3, 'Seamus O’Leary'
union all
select 4, 'Jonathan Stewart'
union all
select 5, 'Benjamin Franklin';
insert into #MonthRangeSelected
select 1, 1, 3, 6
union all
select 1, 2, 7, 9
union all
select 3, 2, 5, 6;
insert into #WeekSelected
select 1, 1, 3
union all
select 3, 1, 4
union all
select 4, 1, 1;
insert into #DaySelected
select 1, 1, 15
union all
select 1, 2, 25
union all
select 2, 1, 12
union all
select 4, 1, 05
union all
select 5, 1, 19;
Query
select v.Id, v.name, combinations.seq, MonthFrom, MonthTo, Week, Day
from #Vendors v
inner join (select m.vendor, m.seq
from #MonthRangeSelected m
union
select w.vendor, w.seq
from #WeekSelected w
union
select d.vendor, d.seq
from #DaySelected d) combinations
on combinations.vendor = v.id
left join #MonthRangeSelected m
on m.Vendor = combinations.vendor
and m.seq = combinations.seq
left join #WeekSelected w
on w.Vendor = combinations.vendor
and w.seq = combinations.seq
left join #DaySelected d
on d.Vendor = combinations.vendor
and d.seq = combinations.seq
where (MonthFrom is not null
or MonthTo is not null
or Week is not null
or Day is not null)
And this is the result:
Id name seq MonthFrom MonthTo Week Day
1 Tom Smith 1 3 6 3 15
1 Tom Smith 2 7 9 NULL 25
2 Bruce Lee 1 NULL NULL NULL 12
3 Seamus O’Leary 1 NULL NULL 4 NULL
3 Seamus O’Leary 2 5 6 NULL NULL
4 Jonathan Stewart 1 NULL NULL 1 5
5 Benjamin Franklin 1 NULL NULL NULL 19

Answer 2

This is more complicated than it sounds. According to the result, you do not want a cartesian product when there are multiple matches in a table. So, you need to take seqnum into account.
select v.Vendor, v.name, coalesce(m.seq, w.seq, d.seq) as Seq,
m.MonthFrom, m.MonthTo, w.Week, d.Day
from Vendors v left join
SMonthRangeSelected m
on v.Vendor = m.Vendor full join
WeekSelected w
on v.Vendor = w.Vendor and m.seq = w.seq full join
DaySelected d
on v.Vendor = d.Vendor and d.seq in (w.seq, m.seq)
where m.Vendor is not null or
w.Vendor is not null or
d.Vendor is not null;
Strange things can happen when using full join, particularly if you want any filtering. An alternative approach uses union all and group by:
select mwd.Vendor, v.name, mwd.seq,
max(MonthFrom) as MonthFrom, max(MonthTo) as monthTo,
max(Week) as week, max(Day) as day
from ((select m.Vendor, m.seq, m.MonthFrom, m.MonthTo, NULL as week, NULL as day
from month m
) union all
(select w.Vendor, w.seq, NULL as MonthFrom, NULL as MonthTo, w.week, NULL as day
from week
) union all
(select d.Vendor, d.seq, NULL as MonthFrom, NULL as MonthTo, NULL as week, d.day
from day d
)
) mwd join
Vendor v
on v.vendor = vmwd.vendor
group by mwd.Vendor, v.vname, mwd.seq;
Note that this version does not require the Vendor table.

Answer 3

You should left outer join to each of the 3 tables, and then include the following in your where clause:
(MonthFrom is not null or Week# is not null or Day# is not null)
it sounds like you can inner join to the Vendor table

Answer 4

I believe that this will do what you need:
SELECT
V.[Vendor#], -- I'll never understand why people insist on using names that require brackets
V.Name,
COALESCE(M.[Seq#], W.[Seq#], D.[Seq#]) AS [Seq#],
M.MonthFrom,
M.MonthTo,
W.[Week#],
D.[Day#]
FROM
Vendor V
LEFT OUTER JOIN MonthRange M ON M.[Vendor#] = V.[Vendor#]
LEFT OUTER JOIN Week W ON W.[Vendor#] = V.[Vendor#]
LEFT OUTER JOIN Day D ON D.[Vendor#] = V.[Vendor#]
WHERE
(
M.[Vendor#] IS NOT NULL OR
W.[Vendor#] IS NOT NULL OR
D.[Vendor#] IS NOT NULL
) AND
(M.[Seq#] = W.[Seq#] OR M.[Seq#] IS NULL OR W.[Seq#] IS NULL) AND
(M.[Seq#] = D.[Seq#] OR M.[Seq#] IS NULL OR D.[Seq#] IS NULL) AND
(D.[Seq#] = W.[Seq#] OR D.[Seq#] IS NULL OR W.[Seq#] IS NULL)

Answer 5

You need full outer joins on the three tables, so as to get all vendor and seq number combinations. Join these with vendor and you are done:
select vendorno, v.name, x.seqno, x.monthfrom, x.monthto, x.weekno, x.dayno
from vendor v
join
(
select vendorno, seqno, m.monthfrom, m.monthto, w.weekno, d.dayno
from monthsel m
full outer join weeksel w using (vendorno, seqno)
full outer join daysel d using (vendorno, seqno)
) x using(vendorno)
order by vendorno, x.seqno;
UPDATE: Without a USING clause the same query get slightly less readable (and thus slightly more error-prone):
select v.vendorno, v.name, x.seqno, x.monthfrom, x.monthto, x.weekno, x.dayno
from vendor v
join
(
select
coalesce(m.vendorno, w.vendorno, d.vendorno) as vendorno,
coalesce(m.seqno, w.seqno, d.seqno) as seqno,
m.monthfrom, m.monthto, w.weekno, d.dayno
from monthsel m
full outer join weeksel w on w.vendorno = m.vendorno and w.seqno = m.seqno
full outer join daysel d on d.vendorno in (m.vendorno, w.vendorno)
and d.seqno in (m.seqno, w.segno)
) x on x.vendorno = v.vendorno
order by v.vendorno, x.seqno;
(Hope I didn't mix things up here. It's easy to make copy & paste errors with such a query. So if it doesn't work properly, look out for typos.)