Union & Pivot multiple tables with different values for similar records - sql

Question

I have multiple tables with the same customer records, but each table has it's own cost currency.
Table 1:
User Country COST_USD
1 USA 10
2 USA 5
3 USA 3
Table 2:
User Country COST_EUR
1 USA 12
2 USA 7
3 USA 5
Table 3:
User Country COST_YEN
1 USA 100
2 USA 50
3 USA 30
What I am looking for is to Union those tables and then pivot the currencies to individual columns (or pivot then union) as follows:
User Country COST_USD COST_EUR COST_YEN
1 USA 10 12 100
2 USA 5 7 50
3 USA 3 3 30
I have tried union all and then pivot but that didn't work since I have differnt currency columns.

Answer 1

Is this what you were thinking of-
select user, country, MAX(COST_USD) COST_USD,MAX(COST_EUR) COST_EUR,MAX(COST_YEN ) COST_YEN
from
(
select user, country, COST_USD, NULL AS COST_EUR, NULL AS COST_YEN from table1
union all
select user, country, NULL AS COST_USD, COST_EUR, NULL AS COST_YEN from table2
union all
select user, country, NULL AS COST_USD, NULL AS COST_EUR, COST_YEN from table3
)T
group by user, country
but if you have many currency columns then you ought to maybe unpivot and union all and the pivot back.
select user, country, currency, amount
from
(select user, country, cost_curr from tableN)U
unpivot
(amount for currency in (COST_EUR, COST_USD,COST_YEN, cost_curr))UPVT
The above is done for all tables and the all resulting unpivots are unioned all and the pivoted back.
As you can see this is quite tedious.
or change you design if possible.

Answer 2

As I mentioned in the comments, this is just a JOIN. Based on your sample data, an INNER JOIN:
SELECT T1.[User], --USER is a reserved keyword, and should not be used for object names
T1.Country,
T1.COST_USD,
T2.COST_EUR,
T3.COST_YEN
FROM dbo.Table1 T1
JOIN dbo.Table2 T2 ON T1.[User] = T2.[User] --USER is a reserved keyword, and should not be used for object names
AND T1.Country = T2.Country
JOIN dbo.Table3 T3 ON T1.[User] = T3.[User] --USER is a reserved keyword, and should not be used for object names
AND T1.Country = T3.Country;
Of course, I doubt all your table have a value for a specific user, so you likely want a FULL OUTER JOIN:
SELECT COALESCE(T1.[User],T2.[User],T3.[User]) AS [User], --USER is a reserved keyword, and should not be used for object names
COALESCE(T1.Country,T2.Country,T3.Country) AS Country,
T1.COST_USD,
T2.COST_EUR,
T3.COST_YEN
FROM dbo.Table1 T1
FULL OUTER JOIN dbo.Table2 T2 ON T1.[User] = T2.[User] --USER is a reserved keyword, and should not be used for object names
AND T1.Country = T2.Country
FULL OUTER JOIN dbo.Table3 T3 ON T3.[User] IN (T1.[User],T2.[User])--USER is a reserved keyword, and should not be used for object names
AND T3.Country IN (T1.Country,T2.Country);
But, like I mentioned, the real solution is fix your design, and have a single table that looks something like this:
CREATE TABLE dbo.YourTable (UserID int,
Country nvarchar(50),
Currency char(3),
Value decimal(12,0));
Then your data would look like this:
INSERT INTO dbo.YourTable
VALUES(1,'USA','USD',10),
(1,'USA','EUR',12),
(1,'USA','YEN',100);
And finally you would get your results with conditional aggregation:
SELECT UserID,
Country,
MAX(CASE Currency WHEN 'USD' THEN Value END) AS COST_USD,
MAX(CASE Currency WHEN 'EUR' THEN Value END) AS COST_EUR,
MAX(CASE Currency WHEN 'YEN' THEN Value END) AS COST_YEN
FROM dbo.YourTable
GROUP BY UserID,
Country;