如何最小化函数中的嵌套级别？

Posted 2023-04-13

【中文标题】如何最小化函数中的嵌套级别？

【英文标题】：How do you minimize the nesting level within a function?

【发布时间】：2017-03-18 16:21:12

【问题描述】：

我目前收到此错误：

消息 217，第 16 层，状态 1，第 127 行 超出最大存储过程、函数、触发器或视图嵌套级别（限制 32）

如何最小化嵌套级别？我做了一些研究，发现有人使用过 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

【参考方案1】：

目前，您的嵌套问题是由于return 格式不正确造成的。

代替：

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

你会使用：

  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');

返回A

由于这是一个标量函数，您可以使用以下方式查询它：

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，函数就应该写成内联表值函数。

如果这不是学习练习，我建议使用人行横道表（正如我的其他答案所解释的那样）。

参考：

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

【讨论】：

如您所说，这纯粹是为了学习练习。接下来我将使用另一个数据库尝试人行横道表。我确实对“等”有疑问。你用过，是什么意思？

@Danny 这是表名EmployeeTransfers 的别名，因此我们不必到处输入EmployeeTransfers 来指定列的表。 from EmployeeTransfers et 与 from EmployeeTransfers as et 相同。这是一个例子：rextester.com/SLLD96236

【参考方案2】：

与其根据具体情况处理所有这些问题，不如创建一个人行横道表？

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');

并在这样的过程中使用它：

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

或者直接从查询中加入它，而不是调用函数。

【讨论】：

我试图掌握用户定义函数的窍门，因为我对它们不太了解。程序我理解的比较清楚。为了将查询与函数连接起来，它是否会是“从 EmployeeTransfers 中选择 EmpFederalFilingStatus = @EmpFederalFilingStatus 和 StateFilingStatus = StateFilingStatus”