how to += in Postgres 9.3 - sql

Question

i am having a trouble to reassign a value, my teacher told me to use something like
var = var + (rest of the query)
but it aint working at all, here it is my code:
create or replace function recorrertablas()
returns void as
$BODY$
declare cursorx cursor for select id, nombre as nombres from tablas;
declare cursory refcursor;
declare rec record;
declare rec2 record;
declare consulta varchar;
--declare consulta2 varchar;
begin
open cursorx;
loop
fetch cursorx into rec;
exit when not found;
consulta= 'create table ' || rec.nombres;
--consulta2= '';
open cursory for select * from atributos where idtabla = rec.id;
loop
fetch cursory into rec2;
exit when not found;
consulta = consulta + '(' || rec2.id || ', ' || rec2.idtabla || ', ' || rec2.nombre || ', ' ||rec2.tipodedatos ;
if rec2.claveprimaria = 1 then
consulta= consulta +', constraint pk_ ' || rec.nombres || '( ' || rec.id || '));';
else
consulta = consulta +');';
end if;
end loop;
close cursory;
end loop;
execute consulta;
close cursorx;
end;
$BODY$
language plpgsql volatile;

Answer 1

If you need to concatenate things use || operator or concat() function like below.
You've been using this operator, but for some reason you mixed it with +.
SELECT 'string' || 'part2';
or
SELECT concat('string', 'part2');
For your specific case:
consulta = consulta || '(' || rec2.id || ', ' || rec2.idtabla || ', ' || rec2.nombre || ', ' ||rec2.tipodedatos ;
if rec2.claveprimaria = 1 then
consulta= consulta || ', constraint pk_ ' || rec.nombres || '( ' || rec.id || '));';
else
consulta = consulta || ');';
When using || operator if any value evaluates to NULL the whole output will be NULL, but when using concat() function it will omit NULL values and still concatenate other arguments.