Conversion failed when converting the nvarchar value 'Internet Explorer 3 original' to data type int

In SQL Server 2008 (TSQL), I've created a stored procedure like this:

CREATE PROCEDURE SP_1_10_2
AS
declare @mostValuableBook nvarchar(255)
SELECT @mostValuableBook = Name
FROM books
WHERE price =
    ( SELECT MAX(price)
      FROM books
      WHERE izd LIKE '%BHV%' );
return @mostValuableBook
GO

But, when I'm trying to execute it:

declare @x nvarchar(255)
EXECUTE @x = SP_1_10_2;
SELECT 'The most expensive BHV book:', @x AS 'Name'
GO

I'm getting an error:

Conversion failed when converting the nvarchar value 'Internet Explorer 3 original' to data type int.

It seems like the problem is in the line

EXECUTE @x = SP_1_10_2;

Can you please tell me what's wrong? Why is it trying to convert to int?

Solution

RETURN cannot be used to return nvarchar / varchar such as you have. RETURN is used to return an integer, this can be expressed as some sort of status code 1=True / 0=False. Read more about return here: http://msdn.microsoft.com/en-us/library/ms174998.aspx

In your case, you simply need to use OUTPUT variables which is similiar to pass-by-ref in C# or C++. You pass the variable to the sproc, the sproc modifies it, and you get the expected results after a SELECT....

Change it so that your parameters becomes an output parameter:

CREATE PROCEDURE SP_1_10_2
@mostValueableBook nvarchar(255) output
AS
SELECT @mostValuableBook = Name
FROM books
WHERE price =
    ( SELECT MAX(price)
      FROM books
      WHERE izd LIKE '%BHV%' );
SELECT @mostValuableBook
GO

Call it like so:

DECLARE @theValBook nvarchar(255)
EXECUTE SP_1_10_2 @mostValuableBook = @theValBook output

Then you can say:

SELECT 'Most expensive book is', @theValBook