ORacle SQL Regular Expressions

Question

I'm looking to create some regular expressions code for some testing. In the below I have created a Constraint Check for an email address.

     create table testemail (username varchar2(50) NOT NULL,
     Password varchar(15) Not NULL,
     CONSTRAINT pk_usertest PRIMARY KEY (username),
     CONSTRAINT un_emailtest CHECK (REGEXP_LIKE(username,'^([[:alnum:]]+)@[[:alnum:]]+.(com|net|org|edu|gov|mil)$'))

Is there a better way to have a constraint check when a new user creating an account?

Also, I'm trying to search a user by the name of 'Luke Haire' but my below sql queries returns no results:

 select * from customers where regexp_like (name, '^([L(u|i|o)ke]+)[\][Haire]$');

Answer 1

I don't really understand your first question. A check constraint is the best way to have a check constraints. That is why databases support it. There are worse ways, such as triggers, but typically the best way is using this built-in, standard capability.

Your specific constraint seems too constrained. Email addresses commonly contain "." and "-" as well.

As for the second question, the problem is the suffix. So try:

select *
from customers
where regexp_like(name, '^([L(u|i|o)ke]+)[\][Haire]@.*$');
---------------------------------------------------^

I should add that I prefer the above to the equivalent:

where regexp_like(name, '^([L(u|i|o)ke]+)[\][Haire]@');

The issue is the difference between like and regexp . like always matches the entire string. So, under most circumstances, I prefer to have regular expressions emulate this by explicitly having the beginning and end. This is to avoid confusion. I use like for simpler searches and regular expressions for more complex ones.

However, I would still expect this to get no matches because \\ is not an allowed character before the @ , according to the check constraint.

Answer 2

Your query doesn't return any rows because you have two mistakes in your pattern.

Second expected character, according to your pattern is \\ so in character list [\\] you should add space [\\ ] or [\\[:space:]] . You are missing quantifier for [Haire] character list. At the moment your pattern works like:

regexp_like ('Luke Haire', '^([L(u|i|o)ke]+)[\](H|a|i|r|e)$')

One possible pattern for your entry string is:

 regexp_like (name, '^([L(u|i|o)ke]+)[\ ][Haire].*$')