Postgres 14

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CREATE TABLE test_calendar (test_date date PRIMARY KEY);
-- fixed
DO
$do$
DECLARE
   i int := 0;
   _date date := '2009-01-01';
BEGIN
   WHILE i <= 10 LOOP
      BEGIN  -- costly noise
         INSERT INTO test_calendar (test_date)
         VALUES (_date + i);
         i := i + 1;
      END;
   END LOOP;
END  -- !
$do$;
-- simpler loop with FOR
DO
$do$
DECLARE
   _date date := '2009-02-01';
BEGIN
   FOR i IN 1..10  -- i defined implicitely
   LOOP
      INSERT INTO test_calendar (test_date)
      VALUES (_date + i);
   END LOOP;
END
$do$;
-- much simpler set-based solution with generte_series()
INSERT INTO test_calendar (test_date)
SELECT generate_series(timestamp '2009-03-01', timestamp '2009-03-11', interval '1 day');
11 rows affected

SELECT * FROM test_calendar;


test_date


2009-01-01

2009-01-02

2009-01-03

2009-01-04

2009-01-05

2009-01-06

2009-01-07

2009-01-08

2009-01-09

2009-01-10

2009-01-11

2009-02-02

2009-02-03

2009-02-04

2009-02-05

2009-02-06

2009-02-07

2009-02-08

2009-02-09

2009-02-10

2009-02-11

2009-03-01

2009-03-02

2009-03-03

2009-03-04

2009-03-05

2009-03-06

2009-03-07

2009-03-08

2009-03-09

2009-03-10

2009-03-11