Stored Function with Multiple Queries and Different Selected Columns - sql

Question

I have series of queries based on a report type. For simplicity here is an example of what i'm trying to do:
If #Reporttype = '1'
Select lcustomerid, lname, fname
from customers
Where dtcreated > #startdate
Else if #Reporttype = '2'
Select barcode, lname, fname
from employees
where dtcreated > #startdate
Else if #reporttype = '3'
Select thetime, lname, name, barcode, lcustomerid
from Customers
where dtcreated > #startdate
You'll notice that I run 3 separate queries, based on the report type being passed. You'll also notice I am returning different columns and the number of columns.
I'd like to make this a stored function, and return the columns I need based on the report type I pass. However, I know that since the number of columns, and the column names are different - that's not going to work as a stored function as I'd like it to.
The major problem here will be reporting this information - I don't want to have separate functions, because i'll have to maintain different reports for each report type.
Is there a way I can make this work?

Answer 1

You can use multi-statement function but you need to specify all columns which will be returned by 3 select statements. It seems it's impossible return multiple result sets.
User-defined functions can not return multiple result sets. Use a
stored procedure if you need to return multiple result sets. https://msdn.microsoft.com/en-us/library/ms191320.aspx
This is one inconvenience but in report you can use only columns you need, others will be nulls.
CREATE FUNCTION MyFun
(
#Reporttype int,
#startdate datetime
)
RETURNS
#Result TABLE
(
lcustomerid int,
lname nvarchar(50),
fname nvarchar(50),
barcode int,
thetime datetime,
name nvarchar(50)
)
AS
BEGIN
If #Reporttype = '1'
insert into #Result (lcustomerid, lname, fname)
select lcustomerid, lname, fname
from customers
Where dtcreated > #startdate
Else if #Reporttype = '2'
insert into #Result (barcode, lname, fname)
Select barcode, lname, fname
from employees
where dtcreated > #startdate
Else if #reporttype = '3'
insert into #Result (thetime, lname, name, barcode, lcustomerid)
Select thetime, lname, name, barcode, lcustomerid
from customers
where dtcreated > #startdate
RETURN
END
So, you can call function in this way
SELECT * FROM dbo.MyFun (1, getdate())

Answer 2

If you cannot use stored procedure and you need to use a function, you can UNPIVOT the data and than in the client side you can PIVOT it.
I need to do something like this when different number of columns are returned to SQL Server Reporting Services report. For example, the following code is always returning three columns - RowID, Column, Value:
DECLARE #Table01 TABLE
(
[ID] INT
,[Value01] INT
,[Value02] NVARCHAR(256)
,[Value03] SMALLINT
);
DECLARE #Table02 TABLE
(
[ID] INT
,[Value01] INT
);
INSERT INTO #Table01 ([ID], [Value01], [Value02], [Value03])
VALUES (1, 111, '1V2', 7)
,(2, 222, '2V2', 8)
,(3, 333, '3V2', 9);
INSERT INTO #Table02 ([ID], [Value01])
VALUES (1, 111)
,(2, 222)
,(3, 333);
-- your function starts here
DECLARE #Mode SYSNAME = 'Table01' -- try with 'Table02', too
DECLARE #ResultSet TABLE
(
[RowID] INT
,[Column] SYSNAME
,[Value] NVARCHAR(128)
);
IF #Mode = 'Table01'
BEGIN;
INSERT INTO #ResultSet ([RowID], [Column], [Value])
SELECT [ID]
,[Column]
,[Value]
FROM
(
SELECT [ID]
,CAST([Value01] AS NVARCHAR(256))
,CAST([Value02] AS NVARCHAR(256))
,CAST([Value03] AS NVARCHAR(256))
FROM #Table01
) DS ([ID], [Value01], [Value02], [Value03])
UNPIVOT
(
[Value] FOR [Column] IN ([Value01], [Value02], [Value03])
) UNPVT
END;
ELSE
BEGIN;
INSERT INTO #ResultSet ([RowID], [Column], [Value])
SELECT [ID]
,[Column]
,[Value]
FROM
(
SELECT [ID]
,CAST([Value01] AS NVARCHAR(256))
FROM #Table02
) DS ([ID], [Value01])
UNPIVOT
(
[Value] FOR [Column] IN ([Value01])
) UNPVT
END;
SELECT *
FROM #ResultSet;
Then in the reporting I need to perform pivot operation again. This is workaround with many limitations:
the unpivot data must be cast to its largest type (usually, string)
unnecessary operations are performed (pivot -> unpivot) instead of just rendering the data;
it does not working well with large amount of data (it is slow)
and others..

Answer 3

For This you may create a scalar value function that return an xml type column and then you can populate that xml tag values to your report screen
CREATE FUNCTION ReportFunc
(
#intReporttype int,
#dtStartdate datetime
)
RETURNS XML
BEGIN
Declare #xmlResult xml
If #intReporttype = '1'
SET #xmlResult = (
select lcustomerid, lname, fname
from customers
Where dtcreated > #dtStartdate
FOR XML PATH (''), TYPE
)
Else if #intReporttype = '2'
SET #xmlResult = (
Select barcode, lname, fname
from employees
where dtcreated > #dtStartdate
FOR XML PATH (''), TYPE
)
Else if #intReporttype = '3'
SET #xmlResult = (
Select thetime, lname, name, barcode, lcustomerid
from customers
where dtcreated > #dtStartdate
FOR XML PATH (''), TYPE
)
RETURN #xmlResult
END

Answer 4

In SQL it is difficult to create something similar so generic or abstract, especially when it has to do with SELECT of colums. If your purpose is to write as less code as you can in order your sql script to be maintained easily and to be able to add new report types in the future with just minor changes I would suggest to use a stored procedure with dynamic sql. You cannot use a function while you wisk your SELECT to be dynamic, its the wrong method. I would write something like that
CREATE PROCEDURE MyProcedure
(
#ReportType int,
#startdate datetime
)
AS
BEGIN
DECLARE #colNames varchar(MAX),#tblName varchar(MAX),#sSQL varchar(MAX);
SELECT #colNames = CASE
WHEN #ReportType = 1 THEN
'lcustomerid, lname, fname' --You can also add alias
WHEN #ReportType = 2 THEN
'barcode, lname, fname'
WHEN #ReportType = 3 THEN
'thetime, lname, name, barcode, lcustomerid'
ELSE
RAISEERROR('Error msg');
END,
#tblName = CASE
WHEN #ReportType = 1 OR #ReportType = 3 THEN
'customers' --You can also add alias
WHEN #ReportType = 2 THEN
'employees'
ELSE
RAISEERROR('Error msg');
END
SET #sSQL =
'Select '+#colNames+'
from '+#tblName +'
where dtcreated > '''+CONVERT(varchar(10), #startdate, 121)+''''
EXEC(#sSQL)
END
And you will call it as
EXEC MyProcedure 1,'20170131'
for example
With this code every time you want a new report type you will need to add just another line in case with the requested column names. I have used this way in working with Crystal reports and I think it is the best possible solution

Answer 5

If you can use Stored Procedures then for maintainability I would look at using a master stored procedure which calls other stored procedures to return different result sets:
CREATE PROCEDURE MyProc_1(#startdate DateTime)
AS
BEGIN
SELECT lcustomerid, lname, fname
FROM customers WHERE dtcreated > #startdate
END
GO
CREATE PROCEDURE MyProc_2(#startdate DateTime)
AS
BEGIN
SELECT barcode, lname, fname
FROM employees where dtcreated > #startdate
END
GO
CREATE PROCEDURE MyProc_3(#startdate DateTime)
AS
BEGIN
SELECT thetime, lname, name, barcode, lcustomerid
FROM Customers WHERE dtcreated > #startdate
END
GO
CREATE PROCEDURE MyProc(#Reporttype char(1), #startdate DateTime)
AS
BEGIN
IF #Reporttype = '1' EXEC MyProc_1 #startdate
ELSE IF #Reporttype = '2' EXEC MyProc_2 #startdate
ELSE IF #reporttype = '3' EXEC MyProc_3 #startdate
END
GO
And to use:
DECLARE #dt datetime = getdate()
EXEC MyProc 1, #dt

Answer 6

CREATE Proc Emp_det
(
#Reporttype INT,
#startdate DATETIME
)
AS
BEGIN
If #Reporttype = '1' BEGIN
Select lcustomerid, lname, fname
FROM customers
WHERE dtcreated > #startdate
END
ELSE IF #Reporttype = '2' BEGIN
Select barcode, lname, fname
FROM employees
WHERE dtcreated > #startdate
END
ELSE IF #reporttype = '3' BEGIN
Select thetime, lname, name, barcode, lcustomerid
FROM Customers
WHERE dtcreated > #startdate
END
END
GO
Exec Emp_det 1,GETDATE()