ERROR: missing FROM-clause entry for table "new" - postgresql

Question

I have a parent table layer_1_ and a number of child tables layer_1_points, layer_1_linestrings etc. which contain some geometry data. Each child table has its own geometry constraint. So, for example, layer_1_points has this constraint:
CONSTRAINT enforce_geotype_geom_geom CHECK (geometrytype(geom) = 'POINT'::text)
Whereas layer_1_linestrings table has this constraint:
CONSTRAINT enforce_geotype_geom_geom CHECK (geometrytype(geom) = 'LINESTRING'::text)
Many other layer tables have similar names: layer_2_, layer_3_, ..., layer_N_. And all of them have their own child tables. What I want to achive is that when a user inserts to a parent table (layer_N_), then this insert statement should be forwarded to a particular child table (layer_N_points etc.). So, for example, when I do:
INSERT INTO layer_1_ (geom) VALUES(ST_GeomFromText('POINT(0 0)', 3857))
I should actually insert to layer_1_points, because geom type is POINT. To achive all this I created this trigger function and the trigger itself:
CREATE OR REPLACE FUNCTION trigger_layer_insert()
RETURNS trigger AS
$$
DECLARE
var_geomtype text;
table_name text;
layer_id text := (TG_ARGV[0])::text;
BEGIN
var_geomtype := geometrytype(NEW.geom);
IF var_geomtype = 'POINT' THEN
table_name := (SELECT concat ('layer_', layer_id, '_points'));
ELSIF var_geomtype = 'MULTIPOINT' THEN
table_name := (SELECT concat ('layer_', layer_id, '_multipoints'));
ELSIF var_geomtype = 'LINESTRING' THEN
table_name := (SELECT concat ('layer_', layer_id, '_linestrings'));
ELSIF var_geomtype = 'MULTILINESTRING' THEN
table_name := (SELECT concat ('layer_', layer_id, '_multilinestrings'));
ELSIF var_geomtype = 'POLYGON' THEN
table_name := (SELECT concat ('layer_', layer_id, '_polygons'));
ELSIF var_geomtype = 'MULTIPOLYGON' THEN
table_name := (SELECT concat ('layer_', layer_id, '_multipolygons'));
END IF;
EXECUTE '
INSERT INTO ' || table_name || '
SELECT * FROM (SELECT NEW.*) AS t
';
RETURN NULL;
END;
$$
LANGUAGE 'plpgsql' VOLATILE;
CREATE TRIGGER trigger_layer_1_ BEFORE INSERT
ON layer_1_ FOR EACH ROW
EXECUTE PROCEDURE trigger_layer_insert(1);
However, when I do actual insert like:
INSERT INTO layer_1_ (geom) VALUES(ST_GeomFromText('POINT(0 0)', 3857))
I get an error message:
ERROR: missing FROM-clause entry for table "new"
LINE 3: SELECT * FROM (SELECT NEW.*) AS t
^
QUERY:
INSERT INTO layer_1_points
SELECT * FROM (SELECT NEW.*) AS t
So, what is wrong with SELECT NEW.* and how can I fix it? Thanks!
EDIT
I also tried this:
EXECUTE '
INSERT INTO ' || table_name || '
SELECT * FROM (SELECT NEW.*) AS t
' USING NEW;
But it has no effect.

Answer 1

When you execute something using PLPGSQL statement EXECUTE it runs in the different context so local variables is not visible there. To pass variable(s) the EXECUTE '<SQL script>' USING <variables list>; form is used:
EXECUTE 'insert into table(field1, field2) values ($1, $2)' USING var1, var2;
So the statement should be:
EXECUTE 'INSERT INTO ' || table_name || ' SELECT * FROM SELECT $1.*) AS t'
USING NEW;
But much more secure is using format function:
execute format('INSERT INTO %I SELECT * FROM SELECT $1.*) AS t', table_name)