 |
|
SQL Server Tips by Burleson |
Foreign Key
A foreign key enforces referential integrity by requiring that the
values from a column either exist in a referenced table or are NULL.
Relationships between tables are established by defining primary
keys or unique keys and referencing them with foreign keys.
Example: To create a one to many relationship between Table1 and
Table2. Table1_ID is the name of the column that is the primary key
from Table1; Table2_f is the foreign key from Table2 that will
relate both tables.
ALTER TABLE dbo.Table2 ADD
CONSTRAINT
FK_Table2_Table1 FOREIGN KEY
(
Table2_f
) REFERENCES dbo.Table1
(
Table1_ID
)
For a one to one relationship, both related columns must be primary
keys. In this example, Table2_f should be a primary key or unique. A
column can be a primary key and a foreign key simultaneously.
The above book excerpt is from:
Super SQL
Server Systems
Turbocharge Database Performance with C++ External Procedures
ISBN:
0-9761573-2-2
Joseph Gama, P. J. Naughter
http://www.rampant-books.com/book_2005_2_sql_server_external_procedures.htm |
