SQL Server-查询数据库以查找两列之间的差异

Question

我试图显示不同蔬菜的每个基本方向（N，E，S，W）的水测量值之间的差异。我认为我走在正确的道路上，但不确定。

这是创建表语句

CREATE TABLE Location
(
     LocationID int IDENTITY(0, 1) NOT NULL
,    LocationExposure varchar(50) NOT NULL
,    LocationSunlightPercentage numeric(3,2) NOT NULL
,    LocationMoistureLevel numeric(3, 2) NOT NULL
,    CONSTRAINT PK_Location PRIMARY KEY (LocationID)
)

CREATE TABLE Crop
(
     CropID int IDENTITY(0, 1) NOT NULL
,    CropName varchar(50)
,    CropOptimalSunlightPercentage numeric(3,2) NOT NULL
,    CropOptimalMoistureLevel numeric(3,2) NOT NULL
,    CropExpectedHarvestWeight numeric(3,2) NOT NULL
,    CONSTRAINT PK_Crop PRIMARY KEY (CropID)
)

CREATE TABLE Sowing
(
     CropID int NOT NULL
,    TechnicianID int NOT NULL
,    LocationID int NOT NULL
,    SowingDate date NOT NULL
,    SowingSeedCount int NOT NULL
,    CONSTRAINT PK_Sowing PRIMARY KEY (CropID, TechnicianID, LocationID)
,    CONSTRAINT FK_SowingCrop FOREIGN KEY (CropID) REFERENCES Crop(CropID) ON DELETE CASCADE
,    CONSTRAINT FK_SowingTechnician FOREIGN KEY (TechnicianID) REFERENCES Technician(TechnicianID) ON DELETE CASCADE
,    CONSTRAINT FK_SowingLocation FOREIGN KEY (LocationID) REFERENCES Location(LocationID) ON DELETE CASCADE
)

这是虚拟数据

INSERT INTO Location VALUES ('East', 0.28, 0.80)
INSERT INTO Location VALUES ('North', 0.17, 0.84)
INSERT INTO Location VALUES ('West', 0.38, 0.48)
INSERT INTO Location VALUES ('South', 0.45, 0.66)

INSERT INTO Crop VALUES ('Carrot', 0.26, 0.82, 0.08)
INSERT INTO Crop VALUES ('Beet', 0.44, 0.80, 0.04)
INSERT INTO Crop VALUES ('Corn', 0.44, 0.76, 0.26)
INSERT INTO Crop VALUES ('Tomato', 0.42, 0.80, 0.16)
INSERT INTO Crop VALUES ('Radish', 0.28, 0.84, 0.02)

INSERT INTO Sowing VALUES (0, 0, 0, '20050418', 28)
INSERT INTO Sowing VALUES (0, 1, 1, '20050414', 14)
INSERT INTO Sowing VALUES (1, 0, 2, '20050418', 36)
INSERT INTO Sowing VALUES (2, 1, 3, '20050414', 20)
INSERT INTO Sowing VALUES (2, 2, 2, '20050419', 12)
INSERT INTO Sowing VALUES (3, 3, 3, '20050425', 38)
INSERT INTO Sowing VALUES (4, 2, 0, '20050430', 30)

并进行查询

SELECT CropName AS [Crop], LocationExposure AS [Location], CropOptimalMoistureLevel AS [Water Needed],  
       LocationMoistureLevel AS [Water Available], 
       CropOptimalMoistureLevel - LocationMoistureLevel AS [Difference]
FROM Sowing S JOIN
     Location L
     ON L.LocationID = S.LocationID JOIN
     Crop C
     ON C.CropID = S.CropID

Answer 1

您不需要Sowing表。您只需要一个CROSS JOIN：

SELECT c.CropName AS [Crop], l.LocationExposure AS [Location],
       c.CropOptimalMoistureLevel AS [Water Needed],  
       l.LocationMoistureLevel AS [Water Available], 
       (c.CropOptimalMoistureLevel - l.LocationMoistureLevel) AS [Difference]
FROM Location L CROSS JOIN
     Crop C
ORDER BY C.CropID, l.LocationExposure;