mysql - How to know if a point is inside a rectangle on the map?

I have four points that represent a rectangle (a,b,c,d). I got these points from mobile GPS.

In my database I have this table of business locations:

bussId | longitude | latitude
-----------------------------
  ..      ..          ..

How can I know which businesses are inside the rectangle?

I want to implement this function:

function isInsideRectangle(Point buss,Point a,Point b,Point c,Point d)

where the Point contains longitude and latitude.