Joining 3 columns from one table to 1 column in another table - sql

Question

I'm trying to join Table1 to Table2 as shown below:
Table1:
| RecCurr | PayCurr | MTMCurr | TradeID |
|---------|---------|---------|---------|
| USD | CAD | JPY | 1234 |
Table2:
+------+-------+
| Curr | Value |
+------+-------+
| USD | 10 |
| CAD | 11 |
| JPY | 12 |
+------+-------+
Joined table:
+---------+---------+---------+---------+----------+----------+----------+
| RecCurr | PayCurr | MTMCurr | TradeID | RecValue | PayValue | MTMValue |
+---------+---------+---------+---------+----------+----------+----------+
| USD | CAD | JPY | 1234 | 10 | 11 | 12 |
+---------+---------+---------+---------+----------+----------+----------+
So far, the only solution I have is the following:
SELECT T1.RecCurr, T1.PayCurr, T1.MTMCurr, T2.RecValue, T3.PayValue, T4.MTMValue
FROM
(SELECT RecCurr, PayCurr, MTMCurr FROM Table1) T1,
(SELECT RecCurr, RecValue FROM Table2) T2,
(SELECT PayCurr, PayValue FROM Table2) T3,
(SELECT MTMCurr, MTMValue FROM Table2) T4
where T1.RecCurr = T2.RecCurr
and T1.PayCurr = T3.PayCurr
and T4.MTMCurr = T4.MTMCurr
Is there a cleaner solution that doesn't require me to join Table2 3 times with Table1?

Answer 1

NOTE: Following works on ASE; me thinks it should work on SQLAnywhere (and IQ) but I don't have a SQLAnywhere db up and running at the moment ...
If you only want to do a single join to Table2 then you'll need a query that performs a table pivot.
First the setup:
create table Table1
(RecCurr char(3)
,PayCurr char(3)
,MTMCurr char(3)
,TradeID int)
go
insert Table1 values ('USD','CAD','JPY',1234)
go
create table Table2
(Curr char(3)
,Value int)
go
insert Table2 values ('USD',10)
insert Table2 values ('CAD',11)
insert Table2 values ('JPY',12)
go
select * from Table1
go
RecCurr PayCurr MTMCurr TradeID
------- ------- ------- -----------
USD CAD JPY 1234
select * from Table2
go
Curr Value
---- -----------
USD 10
CAD 11
JPY 12
An example query with a single join to Table2:
select T1.RecCurr,
T1.PayCurr,
T1.MTMCurr,
T1.TradeID,
sum(case when T2.Curr = T1.RecCurr then T2.Value else 0 end) as RecValue,
sum(case when T2.Curr = T1.PayCurr then T2.Value else 0 end) as PayValue,
sum(case when T2.Curr = T1.MTMCurr then T2.Value else 0 end) as MTMValue
from Table1 T1,
Table2 T2
where T2.Curr in (T1.RecCurr, T1.PayCurr, T1.MTMCurr)
group by T1.RecCurr, T1.PayCurr, T1.MTMCurr, T1.TradeID
go
RecCurr PayCurr MTMCurr TradeID RecValue PayValue MTMValue
------- ------- ------- ----------- ----------- ----------- -----------
USD CAD JPY 1234 10 11 12
And for those with allergies to comma's (in the FROM clause):
select T1.RecCurr,
T1.PayCurr,
T1.MTMCurr,
T1.TradeID,
sum(case when T2.Curr = T1.RecCurr then T2.Value else 0 end) as RecValue,
sum(case when T2.Curr = T1.PayCurr then T2.Value else 0 end) as PayValue,
sum(case when T2.Curr = T1.MTMCurr then T2.Value else 0 end) as MTMValue
from Table1 T1
join Table2 T2
on T2.Curr in (T1.RecCurr, T1.PayCurr, T1.MTMCurr)
group by T1.RecCurr, T1.PayCurr, T1.MTMCurr, T1.TradeID
go
RecCurr PayCurr MTMCurr TradeID RecValue PayValue MTMValue
------- ------- ------- ----------- ----------- ----------- -----------
USD CAD JPY 1234 10 11 12

Answer 2

There is always a better way to write a query when it has commas in the FROM clause. In addition, the subqueries are unnecessary:
SELECT T1.RecCurr, T1.PayCurr, T1.MTMCurr,
T2r.RecValue, T2p.PayValue, T2m.MTMValue
FROM T1 JOIN
Table2 t2r
ON T2r.RecCurr = T1.RecCurr JOIN
Table2 t2p
ON t2p.PayCurr = t1.PayCurr
Table2 t2m
ON t2m.MTMCurr = t1.MTMCurr;