MySQL has been a rare major newcomer to the industry -- pushing down prices of databases and their maintenance.

Widenius said that when large companies start to use MySQL, they usually use it to replace databases running some 60-80 percent of their applications -- creating price pressure also on the databases used for the remaining applications.

MySQL's value to Oracle is much larger than its turnover as it would remove some of the pricing pressure on its own databases, Widenius said.

MySQL pays for the whole Sun acquisition, he said.

Oracle has said it plans to customize its software with Sun's hardware, selling specialized computers and storage devices that offer better performance than ones using hardware and software from other companies.

Open Source Worth a Billion

Sun has lately positioned MySQL as a rival to Microsoft, but Widenius said not one of the large clients use MySQL on Windows, it has always had just a few developers working on Windows, and it has a direct, free rival there.

"This means that there is very little money to be made on the Windows side for MySQL. They are not going to make a profit there. The big money is on the Linux side where MySQL already successfully competes with Oracle, and where MySQL has put all their efforts during the last 10 years," Widenius said.

Two large European clients of MySQL, who wished not to be quoted due to the sensitivity of the matter, told Reuters they have been switching between Oracle and MySQL databases for their different applications, based on changing business needs.

They also said they are worried about the position of the rival database in the future product roadmap of Oracle.

Widenius said he was worried his creation could be killed.

"It is easier to use and it's cheaper -- if cheapness was be removed, the attractiveness decreases," Widenius said.

Donald Feinberg, an analyst at Gartner, said that any attempt by Oracle to kill MySQL would fail, as with open source software others could take the code, re-name it and create their own versions, as has happened before.

Widenius said that while the code could be easily copied, the main problem was the ecosystem around MySQL -- companies making business from it, developing it and using it.

"If it would be easy to fork (copy) it, no-one would have paid a billion dollars for it."