internal table logic

Dear experts,

I have an internal table like below

table A

field 1 field 2

100----

s

100----

r

100----

y

200----

w

200----

z

300----

d

300----

k

300----

u

I need to pick up the single data in field1 like below

internal table b

field1

100

200

300

Can any one give the logic for this

Thanks in advance

karthik