Converting mulitlinestring to linestring in PostgreSQL with PostGIS?

Question

I am using postgres with postgis and I have a set of points which I would like to interpolate with a set of lines.

Now my problem is that the set of lines are of type multilinestring.

Is there a way to convert them to linestring?

Answer 1

This answer shows a great way to convert multi-part to single-part.

Example for converting multilinestring to linestring with SRID 3857:

• Check your table if there is any feature with more than 1 part:

  SELECT COUNT(CASE WHEN ST_NumGeometries(geom) > 1 THEN 1 END) AS multi_geom,
  COUNT(geom) AS total_geom
  FROM my_table;
  

If you see "multi_geom" in the result of the above statement is 0, it's safe to proceed to the next step. Otherwise, when multi_geom is larger than 0, you have features in my_table that can not convert safely to single part, you'll have to resolve those problem by hand before proceeding.

• Convert:

  ALTER TABLE my_table
  ALTER COLUMN geom TYPE geometry(linestring,3857) USING ST_GeometryN(geom, 1);
  

Answer 2

" ST_Dump comes in very handy for expanding a MULTI geometry into single geometries. Below is an example. That expands a set of MULTIPOLYGONs into single POLYGONs

SELECT somefield1, somefield2, (ST_Dump(the_geom)).geom As the_geom FROM sometable "

http://www.bostongis.com/postgis_dump.snippet