Cannot store result into variable SQL

Question

just have a general question today. I am trying to store the result in a variable however it's not working. I am not trying to do anything fancy rather a simple task. See below:

    declare @prizeid bigint;
    declare @today datetime;
    declare @dayOfMonth int;
    declare @year int;
    declare @month int;
    select @today = getdate();
    select @dayOfMonth = Day(@today);
    select @year = Year(@today);
    select @month = Month(@today);

    if @month = 1
    begin
        select @month = 12
        select @year = @year - 1
    end
    else select @month = @month - 1; 




declare @sqlQuery varchar(250);
declare @quantityForSnapShot bigint;
declare @filename varchar(25);

set @prizeid=31
set @filename = 'Prizes_' + REPLACE(STR(@month, 2, 0), ' ', '0') + '_' + ltrim(str(@year));

select @sqlQuery = 'select Quantity from ' + @filename +
' where PrizeID=' + convert(varchar,@prizeid)
EXEC @quantityForSnapShot=@sqlQuery
print @quantityForSnapShot

All I really want is to retreive the Quantity and store it in the var @quantityForSnapShot.

:-)

Answer 1

declare @prizeid bigint;
declare @today datetime;
declare @dayOfMonth int;
declare @year int;
declare @month int;
select @today = getdate();
select @dayOfMonth = Day(@today);
select @year = Year(@today);
select @month = Month(@today);

if (@month = 1)
    begin
        select @month = 12
        select @year = @year - 1
    end
else 
   begin
      select @month = @month - 1; 
   end

declare @sqlQuery nvarchar(MAX);  --<-- to be on safe side
declare @quantityForSnapShot bigint;
declare @filename varchar(25);

set @prizeid=31
set @filename = 'Prizes_' + REPLACE(STR(@month, 2, 0), ' ', '0') + '_' + ltrim(str(@year));

select @sqlQuery = N' select @quantityForSnapShot = Quantity ' +
                   N' from ' + QUOTENAME(@filename) +
                   N' where PrizeID = @prizeid'

EXECUTE sp_executesql @sqlQuery   
                     ,N'@prizeid bigint, @quantityForSnapShot bigint OUTPUT'  
                     ,@prizeid , @quantityForSnapShot OUTPUT

SELECT @quantityForSnapShot

You are trying to call this Dynamic sql as it were a stored procedure with a return value. You will need to use an OUTPUT parameter to retrieve the value of @quantityForSnapShot variable from your dynamic sql.

Also I have used QUOTENAME Function to put square brackets [] around the table name, to tell sql server explicitly that it is an object name. A good practice to get in as it can protect you from Sql injection attack.

Also use system stored procedure sp_executesql to execute dynamic sql.

Answer 2

Try This..

    Begin Tran

    declare @prizeid bigint;
    declare @today datetime;
    select @today = getdate();
    declare @dayOfMonth int;
    select @dayOfMonth = Day(@today);
    declare @year int;
    select @year = Year(@today);
    declare @month int;
    select @month = Month(@today);


    if @month = 1
    begin
    select @month = 12
    select @year = @year - 1
    end
    else select @month = @month - 1; 


    declare @sqlQuery varchar(250);
    declare @quantityForSnapShot bigint;
    declare @filename varchar(25);

    set @prizeid=31
    set @filename = 'Prizes_' + REPLACE(STR(@month, 2, 0), ' ', '0') + '_' + ltrim(str(@year));

    select @sqlQuery = 'select Quantity from ' + @filename +
    ' where PrizeID=' + convert(varchar,@prizeid)
    Set @quantityForSnapShot = @sqlQuery

    Create Table #tmp ( Quantity bigint)

    INSERT INTO  #tmp (Quantity)
    EXEC (@sqlQuery)

    Set @quantityForSnapShot = (Select Quantity From #tmp)
    Select @quantityForSnapShot
          print @quantityForSnapShot

    Rollback Tran