Combine NVARCHAR column with the result of a SUM in SQL Server - sql-server

Question

How can I combine a NVARCHAR column with the result of a SUM in SQL Server?
I have tried
dbo.tblCurrencies.strCurrencySymbol + dbo.tblItems.dcUnitPrice * dbo.tblItems.intItemQuantity
Which tells me:
Error converting data type nvarchar to numeric
So I tried
dbo.tblCurrencies.strCurrencySymbol + CAST(SUM(dbo.tblItems.dcUnitPrice * dbo.tblItems.intItemQuantity) AS NVARCHAR)
AND
CAST(dbo.tblCurrencies.strCurrencySymbol + SUM(dbo.tblItems.dcUnitPrice * dbo.tblSalesOrderItems.intItemQuantity) AS NVARCHAR)
Both tell me
Cannot use an aggregate or a subquery in an expression used for the group by list of a group by clause.
Any more information you need just let me know I'll put it up.
EDIT:
The query
SELECT dbo.tblItems.fkOrder, dbo.tblCurrencies.strCurrencySymbol + SUM(dbo.tblItems.dcUnitPrice * dbo.tblItems.intItemQuantity) AS TotalPrice
FROM dbo.tblCurrencies RIGHT OUTER JOIN
dbo.tblOrders ON dbo.tblCurrencies.pkCurrency = dbo.tblOrders.fkPaysInCurrency RIGHT OUTER JOIN
dbo.tblItems ON dbo.tblOrders.pkOrder = dbo.tblItems.fkOrder
GROUP BY dbo.tblItems.fkOrder
EDIT 2:
Ok I managed to solve it by adding dbo.tblCurrencies.strCurrencySymbol into the group by and using CONCAT()
My query now looks like this:
SELECT dbo.tblItems.fkOrder, { fn CONCAT(dbo.tblCurrencies.strCurrencySymbol, CAST(SUM(dbo.tblItems.dcUnitPrice * dbo.tblItems.intItemQuantity) AS NVARCHAR(10))) } AS TotalPrice
FROM dbo.tblCurrencies RIGHT OUTER JOIN
dbo.tblOrders ON dbo.tblCurrencies.pkCurrency = dbo.tblOrders.fkPaysInCurrency RIGHT OUTER JOIN
dbo.tblItems ON dbo.tblOrders.pkOrder = dbo.tblItems.fkOrder
GROUP BY dbo.tblItems.fkOrder, dbo.tblCurrencies.strCurrencySymbol
It also works without the CONCAT()
SELECT dbo.tblItems.fkOrder, dbo.tblCurrencies.strCurrencySymbol + CAST(SUM(dbo.tblItems.dcUnitPrice * dbo.tblItems.intItemQuantity) AS NVARCHAR(10)) AS TotalPrice
FROM dbo.tblCurrencies RIGHT OUTER JOIN
dbo.tblOrders ON dbo.tblCurrencies.pkCurrency = dbo.tblOrders.fkPaysInCurrency RIGHT OUTER JOIN
dbo.tblItems ON dbo.tblOrders.pkOrder = dbo.tblItems.fkOrder
GROUP BY dbo.tblItems.fkOrder, dbo.tblCurrencies.strCurrencySymbol
Not sure which is better though?

Answer 1

In SQL Server there's a concept named Data Type Precedence. It's there in cases such as these when two different data types need to be combined because there needs to be a method to decide on what the data type of the final output will be.
In your case you're combining NVARCHAR and NUMERIC data types and as NUMERIC has the higher precedence the approach it takes is to try and convert your text data into a number which it can't do, hence the error.
If you need the conversion to run in a way other than defined in the normal precedence order then you need to explicitly make the conversion yourself with either CAST or CONVERT. In your case you need to multiply the needed numbers, convert those to text and then concatenate the currency symbol.
Subsequent errors come from using fields that are neither within an aggregate or specified in the Group By of your select statement. Adding you currency field in there should resolve the other issue assuming you can't have one order with multiple currencies involved.
Putting it all together gives you the following:
SELECT
Orders.fkOrder,
Currencies.strCurrencySymbol
+ CAST(SUM(Items.dcUnitPrice * Items.intItemQuantity) AS varchar(50)) AS TotalPrice
FROM dbo.tblItems AS Items
LEFT OUTER JOIN dbo.tblOrders AS Orders
ON Items.fkOrder = Orders.pkOrder
LEFT OUTER JOIN dbo.tblCurrencies AS Currencies
ON Orders.fkPaysInCurrency = Currencies.pkCurrency
GROUP BY Orders.fkOrder, Currencies.strCurrencySymbol

Answer 2

Based on the query fragment that you have posted, I would try something along the lines of
dbo.tblCurrencies.strCurrencySymbol +
CAST(SUM(dbo.tblItems.dcUnitPrice * dbo.tblSalesOrderItems.intItemQuantity) AS NVARCHAR(x))
Points to note: the cast to NVARCHAR is done on the sum part only
x is the length of the NVARCHAR string that you wish to cast it to (make sure that it is wide enough to hold the largest value that the sum can return).
Using the schema name prior to the column name is deprecated.