what are the guidelines on split shifts. Can an employee be scheduled to work 10am to 2pm and 5pm to 9pm in the same day and be paid only for the hours worked? The business is a restaurant.

Yes. You are guaranteed only two hrs pay for the second reporting.
See "5, b Reporting Time Pay" at the site below, which covers restaurants.

http://www.dir.ca.gov/IWC/IWCArticle5.html

It is a required posting at your restaurant.

And, under certain conditions, you must be paid an additional one hour's pay when you work a split shift. My recollection is that it is when the break between shifts is more than two hours.
http://www.dir.ca.gov/dlse/restaurantrightflyer.pdf

Pattys correct.
I missed it. I seem to remember a break of more than 1 hr is considred a split shift.

Section 4(C)
When an employee works a split shift, one hour's pay at the minimum wage shall be paid in addition to the minimum wage for that workday, except when the employee resides at the place of employment.

If you are schedualed to do a certain shift, and you show up to do this shift,and then you find that your scheduale had been changed, and you start at a later time, so you have to leave and come back, do they have to pay you for showing up at all?

If you report at your last known reporting time, that the company failed to give notice of a change, you would be entitled to the pay.
1/2 of your regular schedule up to 4hrs but no less than 2hrs pay.
Of curse it wouldn't apply OT.