如何为SQL中的每一行创建一个循环？

Question

I have 3 tables ( Users , CourseUsers and Courses which represent the courses assigned to a single user).

I would like to create a procedure which, as soon as I create a new course, will assign this course to every user. What I see I need here is a For each loop to iterate through every user inserting a new row in CourseUsers table

How do I create a loop in SQL?

Answer 1

You don't need a loop.

DECLARE @CourseId INT;

INSERT INTO Courses(Name) VALUES('Some Course');

SET @CourseId  = SCOPE_IDENTITY();

INSERT INTO CourseUsers(UserId, CourseId)
SELECT UserId, @CourseId
FROM Users;

Answer 2

In this case, you don't.

You can issue an insert statement that will insert a new row in that CourseUsers table for every User:

INSERT INTO CourseUsers(CourseId, UserId)
SELECT @CourseId, UserId
FROM Users

SQL is a set-based language: usually you can work on an entire set of data, without the need for loops.

Answer 3

You don't need a loop for doing this.

You can use an INSERT trigger and access the INSERTED logical table, operating on the results of that.

Answer 4

Try -

INSERT INTO CourseUsers (CourseID,UserID)
SELECT 7, UserID FROM Users

Where 7 is your course id (this would obviously change from course to course!).