SAN FRANCISCO - Sun Microsystems Inc. plans to buy open-source software maker MySQL AB for $1 billion, beefing up the server maker's database offerings with a company whose technology is used by some of the world's biggest Web sites.

Santa Clara-based Sun is paying $800 million in cash and assuming $200 million in options to acquire MySQL.

Sun said the deal will help spread MySQL's software to large corporations, which have been the biggest customers of Sun's servers and software, and boost its distribution through Sun's relationships with other server makers such as IBM Corp. and Dell Inc.

MySQL competes with non-open-source offerings from Microsoft Corp. and Oracle Corp., which dominate database software for traditional businesses.

However, MySQL is the rapidly growing market leader in open-source database software, particularly among Web-based companies, where it commands about 80 percent of the global market, according to Sun Chief Executive Jonathan Schwartz.

Microsoft is less than 10 percent of that market, Schwartz said.