Basic T-SQL Question

Question

Let's say I have three tables implemented with a many-to-many relationship. Something like, Person(personID), PersonMovies(personID, movieID), and Movies(movieID). What is the correct way to do multiple inserts in sql server? I would like to insert the person, the movies and then be able to get all of the movies a person owns. So would it be three inserts within a transaction? If so, I would assume the easy part is inserting into the person and movie table, but how would I insert into the PersonMovies table, since that table relies on the existing ID's in the other two tables. I'm assuming that I would insert into Person and Movies, then some way set assign the ID's of the newly inserted tables to a variable from those two tables, then use those variables to insert into the bridge table. I have no idea, but I hope this makes some kind of sense as I'm VERY confused by this!!

Answer 1

I assume that you are having Person and Movies auto increment. If this is the case you need to capture what the key field is after the insert. You can use the scope_identity() function to get the this value. After each insert, save thes to a variable, and then when you isert into PersonMovies, use the saved values.

Answer 2

Begin by inserting the Person record and use SCOPE_IDENTITY to get the unique ID if the inserted record. You can then use this to insert the person's Movies. Before you can insert a persons Movie you need to see whether it exists or not using IF EXISTS. If it does SELECT it from the existing table and assign it's unique ID to a variable. If it doesn't yet exist use the same technique for adding the person and insert the Movie then assign SCOPE_IDENTITY to the movie variable.

In PL/SQL there is an UPSERT statement which combines updating records or inserting them when required. I've added code below for a procedure which does an UPSERT in T/SQL and return the unique ID if a record had to be created.

IF EXISTS (SELECT id FROM dbo.sysobjects WHERE name = 'fts_upsert_team') DROP PROCEDURE fts_upsert_team
GO

CREATE PROCEDURE fts_upsert_team
    @teamID INT OUTPUT,
    @name VARCHAR(100)

AS

    UPDATE 
        fts_teams
    SET
        name = @name
    WHERE
        teamID = @teamID

    IF @@ROWCOUNT = 0
    BEGIN

        INSERT INTO fts_teams
        (
            name
        )
        VALUES
        (
            @name
        )

        SET @teamID = SCOPE_IDENTITY()

    END


GO