SELECT in trigger function in two tables

My table and trigger in PostgreSQL 9.4.3 on x86_64-unknown-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit: CREATE TABLE measurements ( measurement_id SERIAL PRIMARY KEY NOT NULL, measurement_size_in_bytes INTEGER NOT NULL ); CREATE TABLE file_headers ( header_id SERIAL PRIMARY KEY NOT NULL, measurement_id INTEGER NOT NULL, file_header_index_start INTEGER, file_header_index_end INTEGER ); CREATE TRIGGER measurement_ids AFTER INSERT ON measurements FOR EACH ROW EXECUTE PROCEDURE ins_function('SELECT measurement_id FROM measurements ORDER BY measurement_id desc limit 1;', 1, 666 ); where I assumed that the datatype of the SELECT is INTEGER since SERIAL but it is apparently false because I get the error message from this command which starts the trigger: INSERT INTO measurements (measurement_size_in_bytes) VALUES (888);` > ERROR: invalid input syntax for integer: "SELECT measurement_id FROM measurements ORDER BY measurement_id desc limit 1;" > CONTEXT: PL/pgSQL function ins_function() line 10 at assignment ### Edit ins_function() and edits based on @a_horse_with_no_name and @Joishi's comments: CREATE OR REPLACE FUNCTION ins_function() RETURNS TRIGGER AS $$ -- -- Perform AFTER INSERT operation on file_header by creating rows with new.measurement_id, new.file_header_index_start and new.file_header_index_end. -- DECLARE measurement_id INTEGER; file_header_index_start INTEGER; file_header_index_end INTEGER; BEGIN SELECT a.measurement_id INTO measurement_id from measurements a ORDER BY measurement_id desc limit 1; file_header_index_start := TG_ARGV; file_header_index_end := TG_ARGV[1] ; IF TG_OP = 'INSERT' THEN INSERT INTO file_headers (measurement_id, file_header_index_start, file_header_index_end) VALUES (measurement_id, file_header_index_start, file_header_index_end); RETURN NEW; END IF; RETURN NULL; -- result is ignored since this is an AFTER trigger END; $$ LANGUAGE plpgsql; -- -- Function and trigger on INSERT. -- CREATE TRIGGER measurement_ids AFTER INSERT ON measurements FOR EACH ROW EXECUTE PROCEDURE ins_function(1, 666); I get now no error but the output is wrong: no INSERT seen in the table file_headers while successfully in the table *measurements*. ### Output of @ErwinBrandstetter's answer So I started to think about casting from TEXT to INT but this should be so basic operation, since TG_ARGV[] is a datatype of text. One unsuccessful try is format('SELECT $1.%I', TG_ARGV). The regclass could work as you describe here in insaft_function() SELECT NEW.measurement_id, TG_ARGV::regclass, TG_ARGV[1] ::regclass; Why are there no successful INSERTs into the table file_headers?