Customer email address - sql-server

Question

I am new to sql programming. This is for a homework assignment for my database class. I have made all the table I need for the assignment I am just hung up one part. The line in the homework reads as follows:
If type is 'faculty' the email address must end up with '#xxx.edu'
This is what the table looks like:
create table customer
(
CID# char(10) primary key IDENTITY (1,1) NOT NULL,
F_name varchar(20),
M_name varchar(20),
L_name varchar(20),
type varchar(20),
street varchar(20),
city varchar(20),
state varchar(20),
zip char(5),
password varchar (20) NOT NULL,
email varchar(20) NOT NULL
Constraint CK_customer_type check (type in ('student', 'faculty'))
)
Any help someone could lend would be greatly appreciated!

Answer 1

This constraint would check if the email column ends with #xxx.edu.
Constraint CK_email_faculty check (
type<>'faculty' OR
CHARINDEX('#xxx.edu',email)=LEN(email)-LEN('#xxx.edu')+1
)
Remark 1: Better than checking the type being appropriate in a CHECK constraint, make a table customer_type with possible types ('student', 'faculty' ...), and have a foreign key in customer pointing a the type.
CREATE TABLE customer_type(id INT NOT NULL PRIMARY KEY,desc VARCHAR(128));
INSERT INTO customer_type(id,desc)VALUES(1,'student');
INSERT INTO customer_type(id,desc)VALUES(2,'faculty');
Have a foreign key in your customer table to point to the customer_type table:
CREATE TABLE customer(
-- ...
type INT NOT NULL,
-- ...
CONSTRAINT FK_type_customer_type FOREIGN KEY(type) REFERENCES customer_type(id)
)
You would then not insert the type description but the type identifier:
INSERT INTO customer(...,type,...)VALUES(...,1,...); -- for student
INSERT INTO customer(...,type,...)VALUES(...,3,...); -- fails, type doesn't exist
That way you save disk space, and memory when these tables are cached by SQL Server.
Remark 2: The widths of your varchar fields are very small. An email address of only 20 characters?

Answer 2

For your particular case a constraint like this might be ok:
Constraint CK_customer_email check (
type <> 'faculty' OR
email LIKE '%_%#_%.edu'
CHARINDEX('#xxx.edu',email)=LEN(email)-LEN('#xxx.edu')+1
)
This will allow 1+ characters, followed by #, followed by 1+ characters, followed by .edu.
However, in real life (where mean people try to insert bad e-mail addresses), validation is more complex (not all characters are allowed), so a custom function can be used. One that seems to be almost complete is provided here:
CREATE FUNCTION [dbo].[fnAppEmailCheck](#email VARCHAR(255))
--Returns true if the string is a valid email address.
RETURNS bit
as
BEGIN
DECLARE #valid bit
IF #email IS NOT NULL
SET #email = LOWER(#email)
SET #valid = 0
IF #email like '[a-z,0-9,_,-]%#[a-z,0-9,_,-]%.[a-z][a-z]%'
AND LEN(#email) = LEN(dbo.fnAppStripNonEmail(#email))
AND #email NOT like '%#%#%'
AND CHARINDEX('.#',#email) = 0
AND CHARINDEX('..',#email) = 0
AND CHARINDEX(',',#email) = 0
AND RIGHT(#email,1) between 'a' AND 'z'
SET #valid=1
RETURN #valid
END
Then, your constraint would be like this:
Constraint CK_customer_email check (
type <> 'faculty' OR
[dbo].[fnAppEmailCheck] (email) = 1
)

Answer 3

Add Constraint
Constraint CK_email check (email like case when type in ('faculty') then '%#xxx.edu' else email end )