Here is a simple wrapper SQL function.
It checks that the geometry type is a LineString. Other types could be
supported by extension of the SQL.
create or replace function STNumDuplicateVertices( p_geometry geometry,
p_tolerance numeric )
returns integer
language sql
as
$$
select SUM(isDuplicate) as duplicateCount
from (select case when
ST_Distance(ST_PointN(p_geometry,b.*),lead(ST_PointN(p_geometry,b.*))
over (order by b.*)) < p_tolerance
then 1
else 0
end as isDuplicate
from generate_series(1,ST_NumPoints(p_geometry),1) as b
where ST_GeometryType(p_geometry) = 'ST_LineString'
) as f;
$$
select STNumDuplicateVertices(ST_GeomFromText('LINESTRING(0 0 1.1,1
1.001 1.2,1 1.0005 1.3,1 1 1.1,2 2 1.2)',0),0.01);
select STNumDuplicateVertices(ST_GeomFromText('POLYGON((0 0,1 0,1 0,1
1,0 1,0 0))',0),0.01);
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