How to execute SP in for each and union all results? - sql-server

Question

I have a table with certain records, let's call this the Priority table. For each record in this table I need to execute a stored procedure called GetProductsBasedOnPriorityRecord which returns records from a Product table.
All these results need to be returned as one UNION without duplicates.
I'm able to write the following C# pseodo code, but I have no idea on how to do this in SQL:
//DECLARE resultVariable
var products = new List<Product>();
//SELECT * FROM Priority and FOREACH over this
foreach(var prio in Priority) {
//EXEC GetProductsBasedOnPriorityRecord and UNION this on the resultVariable
products.Union(GetProductsBasedOnPriorityRecord(prio));
}
//RETURN resultVariable
return products;

Answer 1

You should not be writing SQL code in loops if you need it to perform even relatively well. But this is what I would do in this case.
-- build some variables
declare #prio table (prio varchar(100) not null)
declare #singlePrio varchar(50)
declare #sqlcmd varchar(50)
-- assuming that the output of the stored procedure is just a table of INTs
declare #output table (outputID int not null)
-- build the list to loop over
insert into #prio (prio)
select * from [Priority]
while exists (select 1 from #prio)
begin
select #singlePrio = (select top 1 prio from #prio)
--
insert into #output exec GetProductsBasedOnPriorityRecord #singlePrio
--
delete from #prio where prio = #singlePrio
end
-- using distinct because you want a 'union' but didnt say 'union all'
select distinct outputID from #output

Answer 2

Well you should be able to do it with a cursor. It's not always the best way. I assume that you are forced to use the existing stored procedure.
Example tables
CREATE TABLE [dbo].[Products](
[ProductID] [int] IDENTITY(1,1) NOT NULL,
[ProductName] [nchar](10) NULL,
[PriorityID] [int] NULL)
CREATE TABLE [dbo].[Priority](
[PriorityID] [int] IDENTITY(1,1) NOT NULL,
[PriorityCode] [nchar](10) NULL)
(with PKs etc).
Sample stored procedure:
ALTER PROCEDURE [dbo].[GetProductsBasedOnPriorityRecord]
-- Add the parameters for the stored procedure here
#PriorityID int = 0
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- Insert statements for procedure here
SELECT * FROM Products WHERE PriorityID = #PriorityID
END
Then something like this:
DECLARE #PriorityID INT
DECLARE #table TABLE (ProductID INT, ProductName NCHAR(10), PriorityID INT)
DECLARE cur CURSOR FOR SELECT PriorityID FROM Priority
OPEN cur
FETCH NEXT FROM cur INTO #PriorityID
WHILE ##FETCH_STATUS = 0
BEGIN
INSERT INTO #table EXEC GetProductsBasedOnPriorityRecord #PriorityID
FETCH NEXT FROM cur INTO #PriorityID
END
CLOSE cur
DEALLOCATE cur
SELECT DISTINCT * FROM #table
Of course this makes some assumptions about your tables. Also (of course) a synthetic example like this is actually showing a long-winded way of doing something very simple.

Answer 3

Try this one -
DECLARE #SQL NVARCHAR(MAX)
IF OBJECT_ID (N'tempdb.dbo.#temp') IS NOT NULL
DROP TABLE #temp
CREATE TABLE #temp (outputID INT NOT NULL)
SELECT #SQL = (
SELECT CHAR(13) + '
INSERT INTO #temp(outputID)
EXEC dbo.GetProductsBasedOnPriorityRecord '''
+ prio + ''''
FROM dbo.[Priority]
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)')
PRINT #SQL
EXEC sys.sp_executesql #SQL
SELECT DISTINCT outputID
FROM #temp