how to make a matrix with all combinations of digits efficiently

[Jean Dubois]

I'd like to generate a matrix like this (small version to give you the idea):

0 0 0 (three columns in this example)
0 0 1
0 0 2
0 0 3
.
.
.
9 9 8
9 9 9

Could anyone here show me how to do this efficiently?

thanks in advance