Question

I have this two tables:

data    
id   |email    
_   
1    |[e-mail]    
2    |[e-mail]    
3    |zzzgimail.com 

errors    
_    
error    |correct    
@gmial.com|@gmail.com    
gimail.com|@gmail.com    

How can I select from data all the records with an email error? Thanks.

Answer 1

SELECT d.id, d.email
FROM data d
    INNER JOIN errors e ON d.email LIKE '%' + e.error

Would do it, however doing a LIKE with a wildcard at the start of the value being matched on will prevent an index from being used so you may see poor performance.

An optimal approach would be to define a computed column on the data table, that is the REVERSE of the email field and index it. This would turn the above query into a LIKE condition with the wildcard at the end like so:

SELECT d.id, d.email
FROM data d
    INNER JOIN errors e ON d.emailreversed LIKE REVERSE(e.error) + '%'

In this case, performance would be better as it would allow an index to be used.

I blogged a full write up on this approach a while ago here.