更好的SQL統計條款數與條款

Question

我有這個查詢，我知道有一個更好的方式來寫它。這裏是查詢命令，以查找庫存中剩下的內容。

DECLARE @reserveDate as Datetime = '10/5/2011 10:20' 

SELECT p.Name 
    , p.Quantity 
    , (SELECT COUNT(*) 
      FROM [Order] o 
     WHERE o.ProductId = p.Id 
      AND o.Completed = 1) as Completed 
    , (SELECT COUNT(*) 
      FROM [Order] o 
     WHERE o.ProductId = p.Id 
      AND o.Completed <> 1 
      AND o.ModifiedDate >= @reserveDate) as Reserved 
    , (SELECT COUNT(*) 
      FROM [Order] o 
     WHERE o.ProductId = p.Id 
      AND o.Completed <> 1 
      AND o.ModifiedDate < @reserveDate) as ReserveExpired 
    --, (Quantity - Completed - Reserved) as Available 
    FROM Product p 

====================================

這裏是一個腳本表

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Order]') AND type IN (N'U')) DROP TABLE [Order] 
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Product]') AND type IN (N'U')) DROP TABLE [Product] 

-- Product -- 
PRINT N' [Product] ' 
CREATE TABLE Product 
    (
     [Id] INT NOT NULL IDENTITY PRIMARY KEY, 
     [Name] NVARCHAR(50) , 
     [Quantity] INT , 
    ); 
SET IDENTITY_INSERT Product ON 
INSERT INTO Product ([Id] , [Name] , [Quantity]) VALUES ('1', 'Tea Package', 7000) 
INSERT INTO Product ([Id] , [Name] , [Quantity]) VALUES ('2', 'Sugar Package', 8000) 
SET IDENTITY_INSERT Product OFF 



-- Order -- 
PRINT N' [Order]' 

CREATE TABLE [Order] 
    (
     [Id] INT NOT NULL IDENTITY PRIMARY KEY , 
     [ProductId] INT , 
     [Completed] Bit, 
     [ModifiedDate] DATETIME 
    ); 
ALTER TABLE [Order] ADD CONSTRAINT FK_Product_Order FOREIGN KEY (ProductId) REFERENCES [Product] (Id) 
GO 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 1, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 1, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 0, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 0, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 0, '10/5/2011 11:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 0, '10/6/2011 11:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (1, 0, '10/6/2011 11:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (2, 1, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (2, 1, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (2, 0, '10/5/2011 10:10' ) 
INSERT INTO [Order] ([ProductId], [Completed], [ModifiedDate] ) VALUES (2, 0, '10/6/2011 10:10' ) 

Answer 1

可以使用替換子查詢：

SELECT p.Name 
     , p.Quantity 
     , SUM(CASE WHEN o.completed = 1 THEN 1 ELSE 0 END) AS Completed 
     , SUM(CASE WHEN o.completed <> 1 AND o.ModifiedDate >= @reserveDate THEN 1 ELSE 0 END) AS Reserved 
     , SUM(CASE WHEN o.completed <> 1 AND o.ModifiedDate < @reserveDate THEN 1 ELSE 0 END) AS ReserveExpired 
     , p.Quantity - 
      SUM(CASE WHEN o.completed = 1 THEN 1 ELSE 0 END) - 
      SUM(CASE WHEN o.completed <> 1 AND o.ModifiedDate >= @reserveDate THEN 1 ELSE 0 END) AS available 
    FROM Product p 
LEFT JOIN ORDER o ON o.productid = p.id 
GROUP BY p.Name, p.Quantity 

或者，下面是等價&更容易閱讀：

SELECT x.name, 
     x.quantity, 
     x.completed, 
     x.reserved, 
     x.reserveexpired, 
     x.quantity - x.completed - x.reserved AS available 
    FROM (SELECT p.Name 
      , p.Quantity 
      , SUM(CASE WHEN o.completed = 1 THEN 1 ELSE 0 END) AS Completed 
      , SUM(CASE WHEN o.completed <> 1 AND o.ModifiedDate >= @reserveDate THEN 1 ELSE 0 END) AS Reserved 
      , SUM(CASE WHEN o.completed <> 1 AND o.ModifiedDate < @reserveDate THEN 1 ELSE 0 END) AS ReserveExpired 
      FROM Product p 
    LEFT JOIN ORDER o ON o.productid = p.id 
     GROUP BY p.Name, p.Quantity) x 

Answer 2

可以T-SQL本身中減去的項目，像：

SELECT A - B AS C FROM TABLE WHERE ID=1

雖然我不知道這樣做的最佳方式與您的子查詢。我也不知道是否需要在編程中保留實際的數量，已完成，保留，& RerservedExpired值，或者如果您只需要這些值來計算可用數量。如果你在SQL之外需要它們，那麼內部的減法將無濟於事。

Answer 3

你可以使用CROSS APPLY/OUTER APPLY運營商：

CREATE INDEX aaa 
ON [Order](ProductId) 
INCLUDE (Completed,ModifiedDate); 

PRINT '***** Sol1 *****' 
SELECT 
    p.Name 
    ,p.Quantity 
    ,ISNULL(ca.Completed,0) Completed 
    ,ISNULL(ca.Reserved,0) Reserved 
    ,ISNULL(ca.ReserveExpired,0) ReserveExpired 
    ,p.Quantity - ISNULL(ca.Completed,0) - ISNULL(ca.Reserved,0) Available 
FROM Product p 
OUTER APPLY 
(
    SELECT 
     SUM(CASE WHEN o.Completed = 1 THEN 1 ELSE 0 END) Completed 
     ,SUM(CASE WHEN o.Completed <> 1 AND o.ModifiedDate >= @reserveDate THEN 1 ELSE 0 END) Reserved 
     ,SUM(CASE WHEN o.Completed <> 1 AND o.ModifiedDate < @reserveDate THEN 1 ELSE 0 END) ReserveExpired 
    FROM [Order] o --WITH(FORCESEEK) or WITH(INDEX=aaa) 
    WHERE o.ProductId = p.Id 
) ca; 

PRINT '***** Sol2 *****' 
SELECT 
    p.Name 
    ,p.Quantity 
    ,ISNULL(q.Completed,0) Completed 
    ,ISNULL(q.Reserved,0) Reserved 
    ,ISNULL(q.ReserveExpired,0) ReserveExpired 
    ,p.Quantity - ISNULL(q.Completed,0) - ISNULL(q.Reserved,0) Available 
FROM Product p 
LEFT MERGE JOIN --or LEFT JOIN 
(
    SELECT o.ProductId 
      ,SUM(CASE WHEN o.Completed = 1 THEN 1 ELSE 0 END) Completed 
      ,SUM(CASE WHEN o.Completed <> 1 AND o.ModifiedDate >= @reserveDate THEN 1 ELSE 0 END) Reserved 
      ,SUM(CASE WHEN o.Completed <> 1 AND o.ModifiedDate < @reserveDate THEN 1 ELSE 0 END) ReserveExpired  
    FROM [Order] o 
    GROUP BY o.ProductId 
) q ON p.Id = q.ProductId;