Create a one to many relationship using SQL Server

Question

how do you create a one to many relationship using SQL Server?

thank you

Answer 1

1. Define two tables (example A and B), with their own primary key
2. Define a column in Table A as having a Foreign key relationship based on the primary key of Table B

This means that Table A can have one or more records relating to a single record in Table B.

If you already have the tables in place, use the ALTER TABLE statement to create the foreign key constraint:

ALTER TABLE A ADD CONSTRAINT FOREIGN KEY fk_b ( b_id ) references b(id)

• fk_b: Name of the foreign key constraint, must be unique to the database
• b_id: Name of column in Table A you are creating the foreign key relationship on
• b: Name of table, in this case b
• id: Name of column in Table B

Answer 2

If you are talking about two kinds of enitities, say teachers and students, you would create two tables for each and a third one to store the relationship. This third table can have two columns, say teacherID and StudentId. If this is not what you are looking for, please elaborate your question.

Answer 3

If you are not using SSMS then here is the syntax:

ALTER TABLE <table_name>
ADD <constraint_name> FOREIGN KEY 
(<column_name1> ,
<column_name2> )
REFERENCES <table_name>
(<column_name1> ,
<column_name2>)

http://infogoal.com/sql/sql-add-foreignkey.htm

Answer 4

This is how I usually do it (sql server).

Create Table Master (
MasterID int identity(1,1) primary key,
Stuff varchar(10)
)
GO
Create Table Detail (
DetailID int identity(1,1) primary key,
MasterID int references Master, --use 'references'
Stuff varchar(10))
GO
Insert into Master values('value')
--(1 row(s) affected)
GO
Insert into Detail values (1, 'Value1') -- Works
--(1 row(s) affected)
insert into Detail values (2, 'Value2') -- Fails
--Msg 547, Level 16, State 0, Line 2
--The INSERT statement conflicted with the FOREIGN KEY constraint "FK__Detail__MasterID__0C70CFB4". 
--The conflict occurred in database "Play", table "dbo.Master", column 'MasterID'.
--The statement has been terminated.

As you can see the second insert into the detail fails because of the foreign key. Here's a good weblink that shows various syntax for defining FK during table creation or after.

http://www.1keydata.com/sql/sql-foreign-key.html