retrieve row number

Hi,

Can I retrieve the row number in a select statement?

For example : if I have the following table “foo”

col1 | col2

-----+-----

 a   | x

 b   | y

 c   | z

select ?? as row_number, col1, col2 from foo;

I should obtain the following result :

row_number | col1 | col2

-----------+------+-----

         1 | a   | x

         2 | b   | y

         3 | c   | z

Thank you

Pascal