Is it possible to substitute a SQL function with a PHP one?

Question

I have a very complex PHP function which would take a lot of time to rewrite in SQL. So I was wondering if it is possible in anyway to do something like that.

For example:

$query = "SELECT p.id FROM pages p WHERE check_access(p.id) = 1"
mysql_query($query);
...

check_access would be the PHP function.

No, sql and php are evaluated in different contexts this is not valid. — Orangepill
– Orangepill, Commented Jun 11, 2013 at 19:27
Have you considered at least trying to re-write the PHP function in SQL? If you're having trouble, you can always post a question on Stack Overflow, if you've put some effort into it. Then again, if it isn't worth your time, just SELECT all the data then filter it in PHP. — user142162
– user142162, Commented Jun 11, 2013 at 19:30
This is quite like asking whether the people on TV can hear you if you shout at the screen :) In this analogy the TV is PHP, and the broadcaster is the DB — Simon at The Access Group
– Simon at The Access Group, Commented Jun 11, 2013 at 20:00

Kevin · Accepted Answer · 2013-06-11 19:33:55Z

2

It is not possible since, SQL interpretion is done separately from PHP interpretion.

You can only use the output of a php function inside an SQL query.

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answered Jun 11, 2013 at 19:33

Kevin

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5 Comments

Simon at The Access Group Over a year ago

As a slight addition to this diagram, it's entirely possible (though not advisable) for the PHP server to be in Japan while the DB it connects to is in Belgium etc - there's no requirement for them to be on a single server or even on the same continent.

Kevin Over a year ago

@Simonatmso.net agreed. But, why is it not advisable anyway?

Simon at The Access Group Over a year ago

If the database is the opposite side of the world to your PHP server then the latency will be NASTY :) Instead of response times of <1ms (assuming same physical server / rack / local network) you would see response times in the order of 200-600ms before you even do any query processing.

Kevin Over a year ago

Do they follow this technique in any web application?

Simon at The Access Group Over a year ago

Most likely not, though in a lesser extent you can put your web servers on a cloud service while having your database within a data-centre which would have a less exaggerated replica of the issue, though in that case if done well the latency would be far more tolerable making it a viable option. Anyway best leave this at that, as this is digressing into a tangent unrelated to the original question :)

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