How do you minimize the nesting level within a function? - sql-server-2008

Question

I'm currently getting this error:
Msg 217, Level 16, State 1, Line 127
Maximum stored procedure, function, trigger, or view nesting level exceeded (limit 32)
How can I minimize the nesting level? I did some research and saw that someone had used go each end but that didn't work for me.
--Function: StateFilingStatus
create function dbo.GetStateFilingStatus(#EmpFederalFilingStatus char(1), #EmpTransferState char(2))
returns char(1)
as
begin
declare #StateFilingStatus char;
if (#EmpTransferState = 'MS')
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'A';
else
set #StateFilingStatus = 'M';
end
else if (#EmpTransferState = 'NJ')
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'B';
else
set #StateFilingStatus = 'A';
end
else if (#EmpTransferState = 'AZ')
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'A';
else
set #StateFilingStatus = 'B';
end
else if (#EmpTransferState = 'CT')
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'F';
else
set #StateFilingStatus = 'M';
end
else if (#EmpTransferState = 'DC')
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'S';
else
set #StateFilingStatus = 'Y';
end
else
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'S';
else
set #StateFilingStatus = 'M';
end
return (select dbo.GetStateFilingStatus(EmpFederalFilingStatus, EmpTransferState) as StateFilingStatus
from EmployeeTransfers)
end
go
select dbo.GetStateFilingStatus('M','NJ') as StateFilingStatus

Answer 1

Currently, your nesting problem is from incorrectly formed return.
Instead of:
return(
select dbo.GetStateFilingStatus(EmpFederalFilingStatus, EmpTransferState) as StateFilingStatus
from EmployeeTransfers
)
You would use:
return #StateFilingStatus;
rextester demo: http://rextester.com/DJM36125
--Function: StateFilingStatus
create function dbo.GetStateFilingStatus(
#EmpFederalFilingStatus char(1)
, #EmpTransferState char(2)
)
returns char(1) as
begin;
declare #StateFilingStatus char(1);
if (#EmpTransferState = 'MS')
begin;
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'A';
else
set #StateFilingStatus = 'M';
end;
else
if (#EmpTransferState = 'NJ')
begin;
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'B';
else
set #StateFilingStatus = 'A';
end;
else
if (#EmpTransferState = 'AZ')
begin;
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'A';
else
set #StateFilingStatus = 'B';
end;
else
if (#EmpTransferState = 'CT')
begin;
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'F';
else
set #StateFilingStatus = 'M';
end;
else
if (#EmpTransferState = 'DC')
begin;
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'S';
else
set #StateFilingStatus = 'Y';
end;
else
begin
if (#EmpFederalFilingStatus = 'S')
set #StateFilingStatus = 'S';
else
set #StateFilingStatus = 'M';
end;
return #StateFilingStatus;
end;
go
select StateFilingStatus = dbo.GetStateFilingStatus('','NJ');
returns A
And since this is a scalar function, you would query with it using:
select
et.EmpFederalFilingStatus
, StateFilingStatus = dbo.GetStateFilingStatus(et.EmpFederalFilingStatus,et.EmpTransferState)
from EmployeeTransfers et
Scalar functions like this can cause horrible performance issues. Whenever possible, functions should be written as in-line table valued functions.
If this is anything except for a learning exercise, I would recommend using a crosswalk table (as my other answer explains).
Reference:
When is a SQL function not a function? "If it’s not inline, it’s rubbish." - Rob Farley
Inline Scalar Functions - Itzik Ben-Gan
Scalar functions, inlining, and performance: An entertaining title for a boring post - Adam Machanic
TSQL User-Defined Functions: Ten Questions You Were Too Shy To Ask - Robert Sheldon

Answer 2

Instead of handling all of this on a case by case basis, why not create a crosswalk table?
create table Filing_State_xwalk (
TransferState char(2) not null
, FederalStatus char(1) not null
, StateStatus char(1) not null
, constraint pk_Filing_State_xwalk
primary key (TransferState, FederalStatus)
);
insert into Filing_State_xwalk values
('MS','S','A')
,('MS',' ','M')
,('NJ','S','B')
,('NJ',' ','A')
,('AZ','S','A')
,('AZ',' ','M')
,('CT','S','F')
,('CT',' ','M')
,('DC','S','S')
,('DC',' ','Y');
And use it in a procedure like so:
set #StateFilingStatus = (
select StateStatus
from Filing_State_xwalk
where TransferState = #EmpTransferState
and FederalStatus = coalesce(#EmpFederalFilingStatus,' ')
);
Or join to it directly from queries instead of calling a function.