ST_Touches Function in Iterative Process

Im a complete newbie to postgis. I have the following problem:

Got two tables:

1. "mp_power_lines_new" -> contains lines of an electricity grid


2. "uw.new"-> contains polygons of all substations in this grid

What I need are the osm_id of the substations which are touching each line.

1. Go to the first line in "mp_power_lines_new"


2. see which substations touch this line


3. fill the osm_id of the substation which touches the line in the first column UW_1


4. fill the second touching substation in column UW_2 and then UW_3 if there is a third one


5. Do this for all rows (lines) in the table "mp_power_lines_new"

Has anyone done something similar or knows a solution?