PostgreSQL select INTO function - postgresql

Question

I am writing a function which will select and SUM the resulting output into a new table-therefore I attempted to use the INTO function. However, my standalone code works, yet once a place into a function I get an error stating that the new SELECT INTO table is not a defined variable (perhaps I am missing something). Please see code below:
CREATE OR REPLACE FUNCTION rev_1.calculate_costing_layer()
RETURNS trigger AS
$BODY$
BEGIN
-- This will create an intersection between pipelines and sum the cost to a new table for output
-- May need to create individual cost columns- Will also keep infrastructure costing seperated
--DROP table rev_1.costing_layer;
SELECT inyaninga_phases.geom, catchment_e_gravity_lines.name, SUM(catchment_e_gravity_lines.cost) AS gravity_sum
INTO rev_1.costing_layer
FROM rev_1.inyaninga_phases
ON ST_Intersects(catchment_e_gravity_lines.geom,inyaninga_phases.geom)
GROUP BY catchment_e_gravity_lines.name, inyaninga_phases.geom;
RETURN NEW;
END;
$BODY$
language plpgsql

Answer 1

Per the documentation:
CREATE TABLE AS is functionally similar to SELECT INTO. CREATE TABLE AS is the recommended syntax, since this form of SELECT INTO is not available in ECPG or PL/pgSQL, because they interpret the INTO clause differently. Furthermore, CREATE TABLE AS offers a superset of the functionality provided by SELECT INTO.
Use CREATE TABLE AS.

Answer 2

Although SELECT ... INTO new_table is valid PostgreSQL, its use has been deprecated (or, at least, "unrecommended"). It doesn't work at all in PL/PGSQL, because INSERT INTO is used to get results into variables.
If you want to create a new table, you should use instead:
CREATE TABLE rev_1.costing_layer AS
SELECT
inyaninga_phases.geom, catchment_e_gravity_lines.name, SUM(catchment_e_gravity_lines.cost) AS gravity_sum
FROM
rev_1.inyaninga_phases
ON ST_Intersects(catchment_e_gravity_lines.geom,inyaninga_phases.geom)
GROUP BY
catchment_e_gravity_lines.name, inyaninga_phases.geom;
If the table has already been created an you just want to insert a new row in it, you should use:
INSERT INTO
rev_1.costing_layer
(geom, name, gravity_sum)
-- Same select than before
SELECT
inyaninga_phases.geom, catchment_e_gravity_lines.name, SUM(catchment_e_gravity_lines.cost) AS gravity_sum
FROM
rev_1.inyaninga_phases
ON ST_Intersects(catchment_e_gravity_lines.geom,inyaninga_phases.geom)
GROUP BY
catchment_e_gravity_lines.name, inyaninga_phases.geom;
In a trigger function, you're not very likely to create a new table every time, so, my guess is that you want to do the INSERT and not the CREATE TABLE ... AS.