split a row into multiple rows based on column values

Hi Gurus,

My table is as below:

op_num       col1         col2           col3                col4

100                0              1               2                    0

200                2             3                0                     1

Required output:

op_num       col1       

100                1

100                2           

200                2

200                3

200                1.

Can you please help me in this.