bien sur on prononce si pour s
"MySQL" is officially pronounced as "My Ess Queue Ell" [maɪ ɛs kjuː ɛl], not "My sequel" [maɪ siːkwəl] [3]. However, the company doesn't mind if others use either the "My sequel" form or other local variations if they are preferred by the speaker.
http://en.wikipedia.org/wiki/MySQL