如何最小化函数内的嵌套级别？

How do you minimize the nesting level within a function?

我目前遇到这个错误：

Msg 217, Level 16, State 1, Line 127
Maximum stored procedure, function, trigger, or view nesting level exceeded (limit 32)

如何最小化嵌套层数？我做了一些研究，发现有人用过 go each end 但这对我不起作用。

--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

为什么不创建人行横道 table？

而不是逐案处理所有这些问题 
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');

然后像这样在程序中使用它：

set @StateFilingStatus = (
  select StateStatus
  from Filing_State_xwalk
  where TransferState = @EmpTransferState
    and FederalStatus = coalesce(@EmpFederalFilingStatus,' ')
);

或者直接从查询连接到它而不是调用函数。

目前，您的嵌套问题是由于格式不正确 return。

而不是：

return(
    select dbo.GetStateFilingStatus(EmpFederalFilingStatus, EmpTransferState) as StateFilingStatus
    from EmployeeTransfers
)

您将使用：

  return @StateFilingStatus;

rextester 演示：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

因为这是一个标量函数，您可以使用它来查询：

select 
    et.EmpFederalFilingStatus
  , StateFilingStatus = dbo.GetStateFilingStatus(et.EmpFederalFilingStatus,et.EmpTransferState)
from EmployeeTransfers et

像这样的标量函数会导致可怕的性能问题。只要有可能，函数应写成内联 table 值函数。

如果这不是学习练习，我建议使用人行横道 table（正如我的其他回答所解释的）。

参考：