我有这个查询,并且我知道有更好的方法来编写它。以下查询对订单进行计数,以找出库存中剩余的数量。
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
======================================
这是表格的脚本
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' )
最佳答案
您可以使用以下方式替换子查询:
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,以下内容是等效的并且更易于阅读:
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
关于sql - 更好的 SQL 计算带有 where 子句的项目数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/7701295/