使用merge-using语句初始化数据库

创建三张表Student、Course、Enrollment

CREATE TABLE [dbo].[Student] (
    [StudentID]      INT           IDENTITY (1, 1) NOT NULL,
    [LastName]       NVARCHAR (50) NULL,
    [FirstName]      NVARCHAR (50) NULL,
    [EnrollmentDate] DATETIME      NULL,
    PRIMARY KEY CLUSTERED ([StudentID] ASC)
)

CREATE TABLE [dbo].[Course] (
    [CourseID] INT           IDENTITY (1, 1) NOT NULL,
    [Title]    NVARCHAR (50) NULL,
    [Credits]  INT           NULL,
    PRIMARY KEY CLUSTERED ([CourseID] ASC)
)

CREATE TABLE [dbo].[Enrollment] (
    [EnrollmentID] INT IDENTITY (1, 1) NOT NULL,
    [Grade]        DECIMAL(3, 2) NULL,
    [CourseID]     INT NOT NULL,
    [StudentID]    INT NOT NULL,
    PRIMARY KEY CLUSTERED ([EnrollmentID] ASC),
    CONSTRAINT [FK_dbo.Enrollment_dbo.Course_CourseID] FOREIGN KEY ([CourseID])
        REFERENCES [dbo].[Course] ([CourseID]) ON DELETE CASCADE,
    CONSTRAINT [FK_dbo.Enrollment_dbo.Student_StudentID] FOREIGN KEY ([StudentID])
        REFERENCES [dbo].[Student] ([StudentID]) ON DELETE CASCADE
)

不会覆盖或删除数据库已经存在的数据，将数据作为一张表更新到另一张表中。

merge into Course as Target
using (values
       (1,'Economics',3),
       (2,'Literrature',3),
       (3,'Chemistry',4)

)
as Source (CourseID,Title,Credits)
on Target.CourseID =Source.CourseID
when not matched by target then
Insert(Title,Credits)
values(Title,Credits);

merge into Student as Target
using(values
     (1,'Tibbetts','Donnie','2013-09-01'),
  (2,'Guzman','Liza','2012-01-13'),
  (3,'Catlett','Phil','2011-09-03')
)
as Source (StudentID,LastName,FirstName,EnrollmentDate)
on Target.StudentID=Source.StudentID
when not matched by Target then
Insert (LastName,FirstName,EnrollmentDate)
values (LastName,FirstName,EnrollmetnDate);

Merge into Enrollment as Target
using (values
       (1,2.00,1,1),
    (2,3.50,2,2),
    (3,4.00,2,3),
    (4,1.80,2,1),
    (5,3.20,3,1),
    (6,4.00,3,2)
)
as Source (EnrollmentID,Grade,CourseID,StudentID)
on Target.EnrollmentID =Source.EnrollmentID
when not matched by Target then
Insert (Grade,CourseID,StudentID)
values (Grade,CourseID,StudentID);