SQL joining 4 tables issue - sql

Question

I have four tables:
T1
ID ID1 TITLE
1 100 TITLE1
2 100 TITLE2
3 100 TITLE3
T2
ID TEXT
1 LONG1
2 LONG2
T3
ID1 ID2
100 200
T4
ID4 ID2 SUBJECT
1 200 A
2 200 B
3 200 C
4 200 D
5 200 E
I want output in this result format:
TITLE TEXT SUBJECT
TITLE1 LONG1 A
TITLE2 LONG2 B
TITLE3 null C
null null D
null null E
So I made this query but it gives me much more results than it should be.On example titles asre displayed more times than just once etc.
SELECT
t1.title,
t2.text,
t4.subject
FROM t1
LEFT OUTER JOIN t2 ON t1.id=t2.id
INNER JOIN t3 ON t1.id1=t3.id1
LEFT OUTER JOIN t4 ON t4.id2=t3.id2
WHERE
t1.id1=100
Thanks for help

Answer 1

Disclaimer: I don't work with DB2. After some browsing through documentation I have found that DB2 supports row_number() and full outer join, but I might easily be wrong.
To get rid of n:m relationship one has to build additional key. In this case simple solution is to add row number to each record in t1 and t4 and use it as join condition. Row_number does just that, produces numbers for groups of data defined by partition by in ascending sequence in order defined by order by.
As there is difference in number of records in t1 and t4, and it is unknown which one always has more records, I use full outer join to join them.
You can see the test (Sql Server version) # Sql Fiddle.
select t1_rn.title,
t2.[text],
t4_rn.subject
from
(
select t1.id,
t1.title,
t1.id1,
t3.id2,
row_number() over(partition by t1.id1
order by id) rn
from t1
inner join t3
on t1.id1 = t3.id1
) t1_rn
full outer join
(
select t4.subject,
t3.id1,
t4.id2,
row_number() over(partition by t4.id2
order by id4) rn
from t4
inner join t3
on t4.id2 = t3.id2
) t4_rn
on t1_rn.id1 = t4_rn.id1
and t1_rn.id2 = t4_rn.id2
and t1_rn.rn = t4_rn.rn
left join t2
on t1_rn.id = t2.id
This kind of work should definitely be done on presentation side of an application, but I believe that software you are using requires already prepared data.

Answer 2

try this :
select t1.title,t2.text,t4.subject
from t4
left join t3
on t4.id2=t3.id2
left join t1
on t1.id1=t3.id1
left join t2
on t1.id=t2.id
where t1.id=100

Answer 3

You should change your tables. Your last join does that to your output -just analyze your query. for every record from T1 you have every record from T4.

Answer 4

Outer joins are guaranteed to replicate rows, instead of matching only the ones you need. You may want to look at this:
http://blog.sqlauthority.com/2009/04/13/sql-server-introduction-to-joins-basic-of-joins/
To understand what the join types are, and how you can use them.
You are looking for a list of subjects, with associated text and title, but this may not be unique; more than one null exist for each of the titles. You want to drive the join from table 4, and get a list of subjects, with associated titles for each.

Answer 5

Looking at your ouput it appears you want all subjects displayed. Knowing this you should first off build everything off this table.
SELECT columns
FROM T4
Next build up your inner joins.
SELECT columns
FROM T4 subjectTable
INNER JOIN T3 mapTable
ON mapTable.ID2 = subjectTable.ID2
When happy with them, add on your optional columns with the outer join.
SELECT columns
FROM T4 subjectTable
INNER JOIN T3 mapTable
ON mapTable.ID2 = subjectTable.ID2
LEFT OUTER JOIN T2 textTable
ON textTable.ID = subjectTable.ID4
LEFT OUTER JOIN T1 titleTable
ON titleTable.ID1 = mapTable.ID1
WHERE
subjectTable.ID = 100;