SQL Server：如何选择现有的ID并将其插入到新的ID字段中

Question

I have two tables Category and Movie and I have a mapping table MovieCategory (a movie can have one or multiple categories).

I then noticed that in my table Movie , there's not one movie with multiple categories.

So I want to delete the MovieCategory mapping table. But first, to accomplish this, I created a new column IDCategory in my table Movie which references the Category (a movie can now have only one single category).

And now, my new IDCategory column is null for all my Movie entries, I want to select all the existing Category entries in my mapping table MovieCategory and then insert the selected IDCategory to my new IDCategory column in the Movie table.

How can I accomplish this?

Here are my columns:

MovieCategory 
---------------------
IDMovie    IDCategory
----------------------

Category table has IDCategory and Movie table has IDMovie and the new IDCategory column

Answer 1

This is just a simple UPDATE statement:

UPDATE M
SET IDCategory = MC.IDCategory
FROM Movie M
     JOIN MovieCategory MC ON MC.IDMovie = M.ID;

This is one of the basics of SQL; I suggest having a read up on the UPDATE syntax: SQL Update Statement & UPDATE (Transact-SQL)