I've built a URL shortener using the Bijective Function algorithm as stated in Stack Overflow. My database table has two columns; ID and URL. For every input URL, the ID is automatically incremented its value is converted to base62. This value forms the slug for the shortened link.
Example: If ID is 42 then its base62 form is g (may differ according to the alphabet set). So the shortened URL is https://example.com/g.
Now I'd like to add custom URL support where the user chooses a custom URL slug. I could create another table to store custom URLs and then check both tables for a matching slug. But this seems rather inefficient.
Can anyone provide an efficient solution?
P.S. I'm using PHP and MySQL.
You could do the reverse mapping of the slug to the corresponding ID it would occupy if it was naturally generated, just keep this in mind:
Before increasing your ID variable you can make sure the entry it would increase to is not already populated by someone who entered a slug which corresponds to that ID, if that's the case just keep incrementing the ID column until you find a new unique value.