An enquirer wrote:

"I'm going to be writing a web page that's going to look up information in a database, and then passing that information back to the customer;  should I learn PHP, Perl, MySQL or some other language?  What about Java?"

If your data is going to be stored in a relational database rather than in plain text files or a directory structure, then you'll need to select MySQL or some other database engine such as Postgres, SQL Server, Oracle, or Sybase, and learn the flavour of SQL that relates to that particular RDBMS.  It's not a foregone conclusion that data should always be stored in a database - but perhaps that's a question for another thread?

Whether or not you need to learn about a database engine and SQL, you'll need to learn a programming language such as Perl, or PHP, or Java, or something else ... or use a piece of software that's already available and can be moulded (configured) to meet your needs.

Considering the three languages mentioned ...

PHP is a language that you emebed within a web page.   You'll choose it if your application is web based, and you think of it as being a series of web pages that happen to include some program-generated content.   Great for those little "one-off" jobs such as voting scripts, or cheking for information from within a file or database.

Perl can also be used to generate web pages, but is very heavily used beyond the web as well.   Setting up the simplest of cases is a little more work, and I would characterise the ideal web application of perl as being first and foremost an appliaction whihc happens to present itself through a browser.  As an example, we have a time card entry system that runs on line, with user logins, time accounting, project and task coding, charging rates, etc ... all of which comes out to a report at the month end.   Perl was (and still would be) the clear choice.

I would suggest you consider Java for large / distributed projects or systems, where you're going to have perhaps a team of staff working on a project and you can get the benefits of the savings that Java will make for you on a really big job; for a smaller, isolated job that Java overhead makes it less that the ideal language.

Having given a grossly simplified comparison,  I'll caution you to look at your own specific circumstances too - both technical and practical issues.  If you have some ide of one of the langauges already, you probably don't want to learn a second.  Check what will be (or what can be) available on the server you'll be using, as that might limit your choice of language.  And finally, if you have a whole lot of colleagues who are PHP geeks and would be thrilled to help you, it would probably be best if you went with PHP rather than ramming Perl or Java down their throats

Similar questions keep cropping up  

Addition to my earlier comparison; to do a relatively small task, you'll find you need to spend a lot more "leaning time" on Perl, but it will be much move powerful and exensible in the end.  If you like using Objects, then Perl has a nice OO interface, to be improved further at Perl 6, whereas the Object stuff in PHP is good but fairly new and still coming along.

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