I know that the variants are more or less the same.. I'd like to know which one you would choose to work with if you have the chance and, if different, the most used one in the IT world. Thanks again.

Thanks mauldinado :-) but seriously, which one should i use? I answer slowly since i am on my mobile.

@Wolf89 - Sql is a standard language (adopted by ISO and ANSI) for acessing relational databases. So any relational database (MySQL, Oralcle, MS SqlServer, Porstgre, etc) accepts SQL comands, but they also have some extra commands (not on SQL ANSI) to help in some difficult or common tasks, like genenerating identifies, some different type of indexes, etc.
So, if you got a good knowledge of plains SQL you can use/work with any relational database without much problem.
If you want to use a specific database, I will recomend MySQL because it´s free and widely used on Internet sites. Of the comercial ones, I still think Oracle is the best one (and the more expensive too).

Start with ANSI SQL, then get Job as Database Admin and see what your employer uses in House. Widly used Databses in the Enterpise field are MSSQL and Oracle. You can get Oracle for testing puposes for free from their Website

To be honest it's more or less the standardized, once you know one SQL it's easy enough to apply it to any other, so pick whatever database system that'll be the most useful/convenient for whatever you want to do

Oh also you can get MS SQL for free too (SQL Server Express Edition), please don't use Oracle if you have a choice, they are an absolutely horrible company

The most important thing is to understand that database programming is not procedural programming. Too many times have I seen SQLcode that is written like C with too many functions in all the wrong places. Set theory is something you must understand, as well as the true cost of logical I/Os, access paths, join methods and proper indexing. Too many people will write crappy code and think that the magical self-tuning, self-administrating RDBMS will take care of everything for them.

Like Kestas, rdrivera2005 and Mauldinado have pointed out, the flavour doesn't really matter; it's getting the basic thinking right.

If you're tree-hugging free spirit who doesn't like capitalists then you should use MySQL as your sandbox. If you're mostly concerned with easy integration with Windows then MSSQL is your tool. If you can live with the vendor being horrible (Kestas, can you please explain?) in return for getting the most advanced RDBMS you should choose Oracle to practice with.

But, it's the basic thinking about how databases work and how important database design is that matters the most.

You can learn ANSI, but it is (in my view) too restrictive, which is why both the MS and Oracle versions have lots of extensions. You can start with ANSI, but a lot of advanced techniques are better implemented using extensions than with core ANSI code, so you'll have to learn a "flavor" of SQL at some point, although as noted the different flavors are generally very similar.

gjdip is correct on SQL being fundamentally different from procedural programming (and object-oriented, of course.) You need to build an intuitive understanding of set theory and how SQL statements work, otherwise your code will be inefficient and buggy.

And whatever you do, don't start with Access, as its SQL implementation is highly irregular. MySQL is a good place to start, as it's on a variety of platforms and is free, but a lot of medium-sized enterprises use MSSQL, and most very large enterprises use Oracle, so keep that in mind.

Do -not- specialize, as it'll pigeon hole you. I can't tell you how many clients I go to that have DBA's that are Oracle specialists trying to do things in DB2 and failing because instead of using standard commands, they try to do oracle short-cuts.

Learn SQL... learn the variety of joins (inners, outers, lefts, rights... when to use when), learn how transactions work, and if you want to go full bore: learn how to make/use stored procedures.

There are free versions of Oracle and MSSQL, too.

>If you can live with the vendor being horrible (Kestas, can you please explain?)
A large part of my Oracle hatred is from my dad, who makes his living as a DBA, working for Ashton Tate, and always hated the way Oracle changed for support while Microsoft charged for the software. It seems like a conflict of interest thing.
My uncle worked for Oracle, and also hated it. Ellison, as I'm sure you're all aware, is king of the douchebags. As for myself I've dived more into open-source databases, particularly MySQL and InnoDB, and at first Oracle bought (and have effectively killed) InnoDB, and now unless the EU pulls off some miracle they'll get MySQL too, leaving the whole thriving open-source database system market in tatters (essentially we'll have to move to Postgresql, but I'm really not sure how that's going to go).
Whereas Oracle have recently only been throwing their huge support-generated money around crushing the smaller companies (including BDB), Microsoft have focused on their own products.

Microsoft are definitely no angels when it comes to bullying small software companies into submission, but in the database arena Oracle *really* takes the cake. Knowing that the database system this software runs on is partly (and soon most likely completely) Oracle software to be stifled makes my future database choices factor in very carefully a move to alternative database systems

*previously working for Ashton-tate, a big DB fanatic, now a successful MS SQL Server and Access consultant (and he would argue that the MS Jet Access backend database has come a long way, and although I don't have the expertise to get into that argument I will say I think a lot of MS Access hatred comes from terrible use of MS Access by end-users, which professional DBAs then have to clean up. I was employed briefly designing an Access system and the horror stories I was expecting never came though for me)

And in case I sound like a pro-MS fanboy, I have actually used SQLite and PostgreSQL far more than any MS database system. My only experience with Oracle was when we had to learn it during a university course, and I didn't enjoy it at all, by far the worst DBMS experience I have yet come across, and I think the reason for this is largely so that they can get support people in to take care of problems and charge companies huge amounts to keep their systems going. That's my impression, and I expect I am biased as hell, but feel free to refute me and I'm sure I'll learn a lot from it

DB2 isn't terrible. mySql is owned by redhat/jboss, I thought? PostGRES is, by far, the most mature of the open source DB offerings.

If you want a tiny in memory DB or a DB to develop locally on, though, there are lots of options.

Transact SQL (Micro$oft SQL Server) is the plavor I use most, but I'm a .Net developer primarily working in ASP.Net on an IIS server, so all Micro$oft products.

Kestas, this is the way big companies do business, isn't it? There was a company named Netscape who are now feeling a bit sorry for themselves because Microsoft could afford to give IE away.

I am not terribly familiar with all the legalese surrounding Oracle's pending ownership of MySQL but isn't MySQL open source? Couldn't anyone develop their own version?

If it is not open source and is a product owned by Sun then Sun owners are profiting from their investments.

There will always be a market for free stuff but is the incentive there for someone to develop and produce it?

For local and free, if you are running M$ Windows in some flavor, SQL Server Express is a free download that is for personal DB work and development. It won't fo replication and only allows one connection at a time, so it isn't for production even on a web server, but for developing an application, it is great as you can be completely disconnected from the world and still work on your project.