join two columns....

i have two files having two columns each. one column is common in each file. How can i join these two files? i pasted two files data into one sheet. But unable to join.

i mean i have columns like this.

col1 col2 col3 col4
a 34 c 45
b 45 a 77
c 15 b 48
d 45 f 15
e 48
f 50

Now how can i get the result like this
a 34 77
b 45 48
c 15 45
d 45 0
e 48 0
f 50 15