-- The table issimple_test is created with two columns.
-- The pid column is a smallint containing the unique
-- identifier for each row. The g1 ST_Geometry column
-- stores the simple and nonsimple geometry samples.

CREATE TABLE issimple_test (pid smallint,
                            g1  ST_Geometry);

-- The INSERT statements insert two records into the issimple_test
-- table. The first is a simple linestring because it
-- doesn't intersect its interior. The second is nonsimple
-- because it does intersect its interior.

INSERT INTO issimple_test VALUES(
   1,
   ST_LineFromText('linestring (10 10, 20 20, 30 30)',1000)
);

INSERT INTO issimple_test VALUES(
   2,
   ST_LineFromText('linestring (10 10,20 20,20 30,10 30,10 20,20 10)',1000)
);

-- The query returns the results of the ST_IsSimple function.
-- The first record returns t (TRUE) because the linestring is simple, while
-- the second record returns f (FALSE) because the linestring is not simple.

SELECT pid, ST_IsSimple(g1) Is_it_simple 
   FROM issimple_test;