SELECT in INSERTING in postgreSQL - postgresql

Question

I have two table Documents and RegCard (name uses a name of current_user)
Table Documents
CREATE TABLE public.document_dimauser
(
documentid uuid NOT NULL,
documentname character varying(100),
author character varying(100),
contents bytea,
CONSTRAINT document_dimauser_pkey PRIMARY KEY (documentid)
)
Table RegCard
CREATE TABLE public.regcard_dimauser
(
regcardid uuid NOT NULL,
documentid uuid,
documentintronumber character varying(100),
documentexternnumber character varying(100),
dateintro date,
dateextern date,
CONSTRAINT regcard_dimauser_pkey PRIMARY KEY (regcardid),
CONSTRAINT regcard_dimauser_documentid_fkey FOREIGN KEY (documentid)
REFERENCES public.document_dimauser (documentid) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
This two tables are connected one row 'documentid'
Also, i have a function, which inserting data in this two tables. Here i try selecting last rec of documentid from first table and transer him in second table
CREATE OR REPLACE FUNCTION public.addrecuserdocuments(
documentname character varying,
contents bytea,
documentintronumber character varying)
RETURNS void AS
$BODY$
DECLARE
comm VARCHAR;
nameuser VARCHAR;
currdate DATE;
iddoc uuid;
BEGIN
SELECT CURRENT_USER INTO STRICT nameuser;
SELECT CURRENT_DATE INTO STRICT currdate;
comm:='INSERT INTO Document_'||nameuser||' VALUES ('||quote_literal(uuid_generate_v4())||', '||quote_literal(documentname)||','||quote_literal(nameuser)||','||quote_literal(contents)||');
SELECT documentid INTO STRICT '||quote_literal(iddoc)||' FROM Document_'||nameuser||' order by documentid DESC LIMIT 1;
INSERT INTO Regcard_'||nameuser||' (regcardid, documentid, documentintronumber, dateintro) VALUES ('||quote_literal(uuid_generate_v4())||' , '||quote_literal(iddoc)||', '||quote_literal(documentintronumber)||', '||quote_literal(currdate)||');';
EXECUTE comm;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
But i have a error
ERROR: query string argument of EXECUTE is null
SQL-состояние: 22004
Контекст: PL/pgSQL function addrecuserdocuments(character varying,bytea,character varying) line 13 at EXECUTE
Please, tell me, what i do wrong?

Answer 1

you concat with || operator - if any value is null the whole string is null...
you can instead do smth like :
comm := format('INSERT INTO %I VALUES(%L)',concat(Document_',nameuser),uuid_generate_v4());
and so on...

Answer 2

Don't concatenate input values if you don't need that, use parameters in the string and use format() to build it. You also don't need variables to store the results of built-in functions and you don't need to "select" the UUID you generated inside your code.
Putting all that together you can simplify your code to:
BEGIN
iddoc := uuid_generate_v4();
comm : = format('INSERT INTO Document_%s VALUES ($1, $2, $3, $4)', current_user);
execute comm
using iddoc, documentname, current_user, contents;
comm := format('insert into regcard_%s (regcardid, documentid, documentintronumber, dateintro) values ($1, $2, $3, $4)', current_user);
execute comm
using uuid_generate_v4(), iddoc, documentintronumber, current_date;
END;
This not only makes the code much more readable it is also a way to prevent SQL injection through that function.
Unrelated, but: I find a design that uses a table with the user name appended highly questionable - especially if that user name is also stored inside the table. If you don't do that you can avoid all that dynamic SQL.