Every single DBMS on the market follows essentially the same basic principles, there is a wide variety of database products on the market, and it is very difficult for a person without solid database background to make a decision on what would be the right product to learn or use. The database market is chockfull of different RDBMS: IBM DB2 UDB, Oracle, Microsoft SQL Server, Sybase, Informix, PostgreSQL, to name just a few.
No two DBMS are exactly alike: There are relatively simple-to-use systems, and there are some that require serious technical expertise to install and operate on; some products are free, and some others are fairly expensive — all in addition to a myriad of some other little things like licensing, availability of expertise, and so on. There is no single formula to help you in the DBMS selection process but rather several aspects to consider while making the choice. Here are the most common ones to start with.
According to a study by Gartner Dataquest, in 2001 the three major DBMS implementations shared about 80 percent of the database market. Oracle accounted for 32 percent, IBM DB2 about 31.6 percent, and Microsoft SQL Server 16.3 percent. Informix (now part of IBM) ranked fourth with 3 percent, followed by Sybase (2.6 percent); the rest of the market (14.4 percent) is shared among dozens (or maybe hundreds) of small vendors and nonrelational "dinosaurs." It's also worth noticing that the share of the "top three" is constantly growing (at the expense of their smaller competitors) — in 1997 the combined share of the "big three" was less than 70 percent.
The prices for the three major implementations are comparable but could vary depending on included features, number of users, and computer processors from under a thousand dollars for a standard edition with a handful of licenses to hundreds of thousands or even millions for enterprise editions with unlimited user access. Many small database vendor implementations are free. Skills are a different story. Database expertise is a costly thing and usually is in short supply. On average, Oracle expertise is valued a little higher than comparable expertise for Microsoft SQL Server or DB2. The total cost of ownership (TOC) analysis released by vendors themselves tends to be biased, so use your best judgment and do your homework before committing your company to a particular vendor. Make no mistake about it: This is a long-term commitment, as switching the database vendors halfway into production is an extremely painful and costly procedure.
One may ask, why spend thousands of dollars on something that can be substituted with a free product? The answer is quite simple: For a majority of businesses the most important thing is support. They pay money for company safety and shareholders' peace of mind, in addition to all the bells and whistles that come with an enterprise level product with a big name. (As the adage goes: "No one was ever fired for buying IBM"....) First, they can count on relatively prompt support by qualified specialists in case something goes wrong. Second, the company management can make a reasonable assumption that vendors like IBM, Microsoft, or Oracle would still be around ten years from now. (Nobody can guarantee that, of course, but their chances definitely look better against the odds of their smaller competitors.) So, the less expensive (and sometimes free) products by smaller database vendors might be acceptable for small businesses, nonprofit organizations, or noncritical projects, but very few serious companies would even consider using them for, say, their payroll or accounting systems.