Declare variable set = select

Question

How do I declare a variable for used in a PostgreSQL 9.3 query?

CREATE or replace FUNCTION public.test()
  returns int4
AS
$BODY$
DECLARE    
    cod_process bigint :=30001;
    cod_instance bigint ;
    utc_log timestamp without time zone := localtimestamp;
    cod_log_type varchar(100) :='information ';
    txt_log_text varchar(100):= 'start process';
    txt_log varchar(100):= txt_log_text||'_'||cod_process;
    set cod_instance= select max(cod_instance) as cod_instance from public.instance where public.instance.cod_process=cod_process;    
BEGIN  
    INSERT INTO public.log (cod_process, cod_instance, utc_log,cod_log_type,txt_log)
    VALUES (cod_process, cod_instance, utc_log,cod_log_type,txt_log );
    RETURN 11;
END;
$BODY$ LANGUAGE 'plpgsql';

ERROR: type "cod_instance" does not exist
SQL state: 42704
Character: 383

Answer 1

You need to run the select using the into clause inside the actual code block, not in the declare block:

begin
   select max(cod_instance) 
      into cod_instance
   from public.instance 
   where public.instance.cod_process=cod_process;

   ....
end;

It's usually not such a good idea to give variables (or parameters) the same name as columns in the table. There are certain cases where this can confuse the parser. To avoid any potential problems, try to use different names for your variables, e.g. by prefixing them (e.g. l_cod_process instead of cod_process or l_cod_instance instead of cod_instance)

More details on variable assignment can be found in the manual: http://www.postgresql.org/docs/current/static/plpgsql-statements.html