如何为 SQL Server 创建用户定义函数

Question

不过，这是一个相当温和的问题

我有一个相当大的存储过程，我正在尝试简化它以提高可读性

它包含许多带有如下图1所示语句的联合子句

图1

SELECT COUNT(1) AS Total
  FROM Orders 
  WHERE (NOT EXISTS (
      SELECT 1 
        FROM (
          SELECT Id 
            FROM OrderLineItems 
            WHERE Orders.Id = Order_Id) AS Sub
        WHERE EXISTS (
            SELECT 1 
              FROM NormalizedLineItems 
              WHERE (Sub.Id = OrderLineItem_Id)
                AND (OutOfStock = 1))))
    AND (EXISTS (
      SELECT 1 AS Total
        FROM OrderShipments 
        WHERE (Orders.Id = Order_Id)
          AND (CarrierApproved = 0)))
    AND (IsQuote = 0)
    AND (Cancelled = 0)
    AND (Archived = 0)
    AND (Completed = 0)
    AND (Holding = 0)

但是每个语句中都有很多重复出现的模式

以下模式多次出现图2

图2

  WHERE (NOT EXISTS (
      SELECT 1 
        FROM (
          SELECT Id 
            FROM OrderLineItems 
            WHERE Orders.Id = Order_Id) AS Sub
        WHERE EXISTS (
            SELECT 1 
              FROM NormalizedLineItems 
              WHERE (Sub.Id = OrderLineItem_Id)
                AND (OutOfStock = 1))))

我试图（出于可读性目的）减少主存储过程中的代码

所以我认为id性能测试是一个UDF，我想出了下面的图3

图3

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION TestFunction (@OrderId int)
RETURNS TABLE
AS
  RETURN
  (
  -- Add the SELECT statement with parameter references here
  SELECT 1 AS Total
    FROM (
      SELECT OrderLineItems.Id AS Id
        FROM OrderLineItems
        WHERE @OrderId = Order_Id) AS Sub
    WHERE EXISTS (
        SELECT 1 AS Total
          FROM NormalizedLineItems
          WHERE (Sub.Id = OrderLineItem_Id)
            AND (OutOfStock = 1)))
GO

尽管上述所有编译，我不确定我是否在正确的轨道上，我在尝试将上述 UDF 应用于原始查询时遇到各种问题

我想知道是否有人可以给我一个具体示例，说明如何将 Fig.2 从 Fig.1 抽象为 UDF，这样我至少可以对解决方案进行性能测试，看看它是否值得

注意：我知道用户定义的函数可能是一场性能噩梦，但我什至还没有到可以测试的阶段

谢谢

Answer 1

创建一个 order_ids 表，其中只有一个名为 order_id 的列

Insert into order_ids
select order_id from 
  FROM Orders 
  WHERE (NOT EXISTS (
      SELECT 1 
        FROM (
          SELECT Id 
            FROM OrderLineItems 
            WHERE Orders.Id = Order_Id) AS Sub
        WHERE EXISTS (
            SELECT 1 
              FROM NormalizedLineItems 
              WHERE (Sub.Id = OrderLineItem_Id)
                AND (OutOfStock = 1))))

然后你可以像这样简化你的Sql：

SELECT COUNT(1) AS Total
  FROM Orders 
  join order_ids
  on order_ids.order_id = Orders.order_id
 ...

如果您的重复语句仅在一个查询中， Common Table Expression是最好的选择：

with CTE_order_ids as
(select order_id from 
  FROM Orders 
  WHERE (NOT EXISTS (
      SELECT 1 
        FROM (
          SELECT Id 
            FROM OrderLineItems 
            WHERE Orders.Id = Order_Id) AS Sub
        WHERE EXISTS (
            SELECT 1 
              FROM NormalizedLineItems 
              WHERE (Sub.Id = OrderLineItem_Id)
                AND (OutOfStock = 1))))
)
SELECT COUNT(1) AS Total
  FROM Orders 
  join CTE_order_ids 
  on order_ids.order_id = Orders.order_id
 ...