geometry - Convert lineString to MultilineString in PostGIS

How can I convert the line string to multiline string in PostGIS? I have converted geometry points to line string by this: st_makeline(location.shape) but by this command:

  SELECT uuid_generate_v4()                                         AS uuid,
          j."deviceId",

         st_astext(st_linemerge(st_union(j.shape))) AS multiLine
  FROM j
  group by date, j."deviceId" ;

I got this results:

It's result is again line string?

Answer

Have you tried ST_Multi? https://postgis.net/docs/ST_Multi.html

select st_astext(st_multi(st_geometryfromtext('LINESTRING (30 10, 10 30, 40 40)')))

MULTILINESTRING((30 10,10 30,40 40))

For you this would be

 SELECT uuid_generate_v4()                                         AS uuid,
      j."deviceId",
     st_astext(st_multi(st_linemerge(st_union(j.shape)))) AS multiLine
FROM j
  group by date, j."deviceId" ;