Difference between : and ! in julia dataframe

I am confusing with difference between : and ! on Julia dataframe.

For example, here is a dataframe:

df = DataFrame(Data1 = rand(5), Data2 = rand(5));

Than, both operations which are,

df[:, 1]

AND

df[!,1]

returns same result on Julia dataframe.

Is there any difference between ! and : ?