SQL - join tables on multiple columns - sql

Question

I want to join few tables:
table1:
A B_key B_version C D
123 abc 1 ccc 11
123 abc 2 ddd 11
456 dfg 1 rrr 22
789 vvv 1 55
table2:
A E F
123 s 5
456 r
111 t 2
table3:
B_key B_version G
abc 1 aa
abc 1 bb
abc 2 aa
abc 2 cc
dfg 1 aa
so the result would look like this:
A B_key B_version C D E F G
123 abc 1 ccc 11 s 5 aa
123 abc 1 ccc 11 s 5 bb
123 abc 2 ddd 11 s 5 aa
123 abc 2 ddd 11 s 5 cc
456 dfg 1 rrr 22 r aa
789 vvv 1 55
Version can go as high as 8.
IF I don't have A, B_key or B_version - the line is useless. Otherwise I need to keep all the information I do have.
In reality I have many more columns.
I've tried:
SELECT table1.A, table 1.B_key, table 1.B_version, table 1.C, table 1.D,
table2.E, table2.F,
table3.G
FROM table1
LEFT JOIN table2
ON table1.A = table2.A
LEFT JOIN table3
ON table1.B_key = table3.B_key AND
table1.B_version = table3.B_version
and the same with FULL JOIN.
It ends up the same: for every B_key only the highest B_version is kept, while the others disappear.
How can I avoid loosing information?

Answer 1

You can use left joins among tables as below :
select t1.A, t1.B_key, t1.B_version, t1.C, t1.D, t2.E, t2.F, t3.G
from table1 t1
left join table2 t2 on t2.A = t1.A
left join table3 t3 on t3.B_key = t1.B_key and t3.B_version = t1.B_version
Demo
in order to bring also the rows for unmatched values for join conditions.

Answer 2

If I understand correctly, you want all the b_keys and b_versions from table1 and table3. Then you want to bring in the other data. That suggests left joins
select . . .
from ((select B_key, B_version
from table1
) union -- on purpose to remove duplicates
( select B_key, B_version
from table3
)
) bb left join
table1 t1
on t1.b_key = bb.b_key and
t1.b_version = bb.b_version left join
table2 t2
on t2.a = t1.a left join
table3 t3
on t1.b_key = bb.b_key and
t1.b_version = bb.b_version;