how to plot 3D surface from a data file in Matlab

I have a data file with 3 columns, x, y, z and I would like to do a 3D plot to visualize the surface.

I could have used meshgrid, but the problem is that I only have data for those y that y<=x. Is there a way to do it?

An example:

x    y    z
============
1    1    0.5
2    1    0.3
2    2    1.2
3    1    1.1
3    2    8.0
3    3    1.4
============