Yes, it's not an April Fool, but it has been announced officially at this site. Oracle is buying Sun for $9.50 per share in cash, which will be approximately $7.4 billion, lot bigger than amount of money spent by Sun to buy MySQL.
Why does Oracle interested in Sun? Because most of Oracle's product are based on Java, so by owning Sun, which developed Java, they can invest more money to make it more compatible and robust for their own products. Besides Java, one of the product that might be interesting for Oracle is Solaris. We might see more Solaris running Oracle in the future