a simple table:
ID, NAME, POST_ID, GROUP_ID
either POST_ID or GROUP_ID must be set, but never both of them, NEITHER none of them. So,
there are valid cases:
ID, NAME, POST_ID, GROUP_ID
x, y, 1, NULL
x, y, NULL, 4
and NOT VALID cases:
ID, NAME, POST_ID, GROUP_ID
x, y, NULL, NULL
x, y, 4, 4
is it possible to set such complicated restriction rule?