-- The startpoint_test table is created with the gid integer column,
-- which uniquely identifies the rows of the table,
-- and the ln1 ST_LineString column.

CREATE TABLE startpoint_test (gid integer,
                              ln1 ST_LineString);

-- The INSERT statements insert the ST_LineStrings into the ln1 column.
-- The first ST_LineString does not have Z coordinates or measures,
-- while the second ST_LineString has both.

INSERT INTO startpoint_test VALUES( 
   1, 
   ST_LineFromText('linestring (10.02 20.01,23.73 21.92,30.10 40.23)', 1000) 
);

INSERT INTO startpoint_test VALUES( 
   2, 
   ST_LineFromText('linestring zm (10.02 20.01 5.0 7.0,23.73 21.92 6.5 7.1,30.10 40.23 6.9 7.2)', 1000) 
);

-- The ST_StartPoint function extracts the first point of each ST_LineString.
-- The first point in the list doesn't have a Z coordinate or a measure
-- while the second point has both because the source linestring does.

SELECT gid, ST_StartPoint(ln1) Startpoint 
   FROM startpoint_test;