The ST_X() function

The x_test table is created with two columns: gid, which uniquely identifies the row, and the pt1 point column:

CREATE TABLE x_test (gid integer,
                     pt1 ST_Point);

The following INSERT statements insert two rows. One is a point without a Z coordinate or a measure. The other column has both a Z coordinate and a measure:

INSERT INTO x_test VALUES( 
   1, 
   ST_PointFromText('point (10.02 20.01)', 1000) 
);

INSERT INTO x_test VALUES( 
   2, 
   ST_PointFromText('point zm (10.02 20.01 5.0 7.0)', 1000) 
);

The query retrieves the values in the gid column and the DOUBLE PRECISION X coordinate of the points:

SELECT gid, ST_X(pt1) x_coord 
   FROM x_test;

        gid        x_coord 

          1 10.02000000000
          2 10.02000000000