How to fix LOOP error PostgreSQL while trying to Select - sql

Question

Here is the code I'm Testing :
DO $$
DECLARE
i INT := 0;
BEGIN
WHILE i <= numberUsers
BEGIN
SELECT COUNT(*) FROM "Users";
SET i := i + 1;
END;
END $$;
But when I try to execute it it return me this error :
ERREUR: « LOOP » manquant à la fin de l'expression SQL
LIGNE 7 : SELECT COUNT(*) FROM "Users";
Kind Regards !

Answer 1

You have considerable structural errors in your code block:
DO $$
DECLARE
i INT := 0;
BEGIN
WHILE i <= numberUsers --<<< numberUsers is undefined and uninitialized
BEGIN --<<< this starts a nested block should be LOOP
SELECT COUNT(*) FROM "Users"; --<<< in a block you must tell plpgsql what to do with the result
SET i := i + 1; --<<< assignment does not use SET in plpgsql
END; --<<< terminated nested block, should terminate loop
END $$;
Correcting all the points from the block becomes:
do $$
declare
i int := 0;
numberusers int;
begin
select count(*)
into numberusers
from "users";
while i <= numberusers
loop
i := i + 1;
end loop;
end $$;

Answer 2

Per:
https://www.postgresql.org/docs/current/plpgsql-control-structures.html#PLPGSQL-CONTROL-STRUCTURES-LOOPS
WHILE boolean-expression LOOP
statements
END LOOP [ label ];
You need the LOOP END ... LOOP portions of the statement.

Answer 3

The error message tells you that something is missing from the expression, which is a clear indication that you have a syntax error. Try this code:
DO $$
DECLARE
i INT := 0;
BEGIN
WHILE i <= numberUsers LOOP
BEGIN
SELECT COUNT(*) FROM "Users";
SET i := i + 1;
END LOOP;
END $$;
Read more here: https://www.postgresqltutorial.com/plpgsql-while-loop/

Answer 4

DO $$
BEGIN
DECLARE
i INT := 0;
BEGIN
WHILE i <= numberUsers LOOP
SELECT COUNT(*) FROM "WU_Users";
i := i + 1;
END LOOP;
END $$;
But it's returning me this now :
psql:matching.sql:12: ERREUR: label de fin « matching » spécifié pour un bloc sans label
LIGNE 12 : END matching $$;