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    <p>First and foremost, <strong>make sure you have unicity constraints in place</strong> on the <code>ID</code> and <code>short_url_code</code> columns.</p> <p>When someone creates a new link:</p> <ol> <li>Get the next largest link <code>ID</code> from the database (<strong>for performance reasons you should really REALLY use <code>autoincrement</code> or <code>SEQUENCE</code></strong>, depending on what your RDBMS offers; otherwise go ahead and select <code>MAX(ID)+1</code> )</li> <li>Generate a short URL code (<code>http://website.com/[short url name]</code>) from <code>ID</code> using <code>base64_encode</code> or <em>any</em> other custom or standard encoding scheme</li> <li>Insert into the <code>links</code> table: <code>ID, short_url_code, destination_url</code></li> <li><p>If the insert fails because of a constraint violation go back to step 1 to try a new <code>ID</code>; you may have had a violation because:</p> <ol> <li>the same ID has already been used (i.e. inserted) in parallel by another thread/process etc. (this will <em>not</em> happen if you used <code>autoincrement</code> or <code>SEQUENCE</code>, and may happen quite often otherwise), and/or</li> <li>the same <code>short_url_code</code> has already been used as a custom URL (this will happen very seldomly unless someone is trying to cause trouble on your site)</li> </ol></li> <li><p>If the insert succeeded, commit and return the short URL to the user</p></li> </ol> <p>When someone creates a new link and passes a custom short URL:</p> <ol> <li>Perform the same step 1 as above</li> <li><strong>Instead of generating</strong> the short URL part from <code>ID</code> as in step 2 above, <strong>use the custom <code>short_url_code</code> provided by the user</strong></li> <li>Perform the same step 3 as above</li> <li>If the insert failed because of: <ol> <li>a constraint violation on <code>ID</code>: go back to step 1 to try a new <code>ID</code></li> <li>a constraint violation on <code>short_url_code</code>: return an error to the user asking him to pick a different custom URL, as the short URL he/she provided has already been used</li> </ol></li> <li>Perform the same step 5 as above</li> </ol>
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    1. COThanks Vlad. I should have mentioned that I was already handling constraint violations. I've switched to base32 which lets me convert a custom url into a number and insert that as the ID. This makes it easy because I only have to have ID as the primary key. If there is a constraint violation for the base32 representation of a custom name it tells them that name is already taken. If there is a constraint violation for a non-custom url, it just keeps incrementing the ID until it can insert. Does that sound like a decent solution?
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    2. COdepends on what tradeoffs you are willing to make; most database native `int` types are at most 64 bits long (the `bigint` or equivalent type), which means that if I provide you with a custom short URL that's longer than 64/5=12 (5=log2(32)) characters you will not be able to accomodate me. Would it be acceptable to not allow users to provide custom URLs longer than 12 characters?
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    3. COGood point. I do need more than 12 characters. How about this: When creating the link, if the custom name is more than 12 characters then I just use a next biggest ID (excluding IDs of custom name links). If it is less than 12 characters I encode the custom name in the ID. Then when looking up a link by its short name, if that ID is not found in the DB that means it was more than 12 chars, so then I just look it up by it's short name.
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