Hi,
I know what is the database is and what is it for. But i can find many databases like sql, oracle, mssql, access and many more. Which of these database is a best one for handling more users for a large organization? Also whats is the difference between mysql and sql?
Which one is giving a free express edition?
What is pc-based databases and others?

Are you asking this question in a professional capacity? If so then it seems obvious that you aren't qualified to make such decisions yourself. If you want to develop a database strategy for your company then I suggest you first hire someone to help you. There is no quick answer about which Database Management System (DBMS) is "best" for your circumstances.

Access is not a DBMS. It is an application development tool.

MySQL is just one example of a DBMS that uses the SQL language. Others are Oracle and Microsoft SQL Server. MySQL, Oracle and Microsoft SQL Server all have versions that are free to download.

sql server is microsoft database and only supported platform is windows.
sql server and windosws is not good for handling more users.
sql express have limitations one processor and max database is 4GB.

oracle express have limitations as sql server.
oracle standard edition have limitation about processor(2 or 4), and enterprise edition is very expensive.

in your case I suggest mysql or postgresql and FreeBsd as operating system, because this OS can handling many users.

if you have much money then oracle on solaris.

I think he's asking this in a "I'm a student and I want someone to do my homework" capacity.

The most common RDBMS for large organizations includes Oracle, MySQL, and SQL Server to a smaller extent.

When you are asking about the difference between MySQL and SQL, I am assuming you mean SQL Server, not SQL the query language. If so, the biggest difference is that MySQL is free and can be used on basically all operating systems, while SQL Server is pretty much limited to the Microsoft OS.

Absolutely false.
SQL Server is capable of handling terabyte-sized databases with hundreds or thousands of users. It is cost-effective and requires minimal administrative overhead.
Please don't make statements about technologies in which you do not have experience.
MySQL requires considerable administrative overhead, similar to Oracle, though both are capable of handling large multi-user applications as well. MySQL is free, but lacks the features of more advanced database servers such as Oracle and SQL Server. MySQL is satisfactory for simple database designs.

Hold on, now, if we didn't allow people to make completely unfounded sweeping generalizations, we'd have to shut down virtually all of the trade magazines, IT educators, tech blogs...

not to mention anything ever said by a politician about the difficulties of being homeless or even just out of work, or a "man of the cloth" about marriage problems, et cetera...

about administartion is true.
sql server can handling and more, but you need better and higher hardware in ratio of other database such as oracle.I tested sql server, oracle, mysql, postgresql.
sql server is very slow in ratio of other databases.

in real world max. database on sql server is under 2 TB, because nobody dare using sql server for bigger databases.

most financial institutions using oracle, db2 or sybase.
and for OS using unix.
I don't know, maybe you are MS boy??

this is wrong!

Then the problem was with your testing.

Actually, many financial institutions are moving away from Oracle, usually to SQL Server or MySQL, because of Oracle's recent increase in licensing fees.

SQL Server, Oracle, MS Access, MySQL. From your SIG I can see that you are simply one of the anti-MS crowd. You don't list SQL Server as one of the platforms in which you have experience, but that apparently does not prevent you from making generalizations about it....

don't be ludicrous, you look like a fool

To be fair, I don't think he actually meant that MySQL is UNsatisfactory for simple designs....

I'm calling you out. Post your test procedures and results.

Independently scrutinised industry-standard benchmarks contradict you there.
SQL Server 2008: Benchmarks

It's very easy to write your own tests but how many different hardware configurations have you actually tested?

That might have been an arguable position 5 years ago, but not today. I know of and have worked with some of those listed here:
SQL Server 2008: Case Studies