SQLite 3.39

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CREATE TABLE tablename (`id` INTEGER, `idg` INTEGER, `typ` INTEGER);
✓
INSERT INTO tablename (`id`, `idg`, `typ`) VALUES
  ('1', '1', '1'),
  ('2', '1', '1'),
  ('3', '1', '1'),
  ('4', '1', '1'),
  ('5', '1', '1'),
  ('6', '1', '1'),
  ('7', '1', '1'),
  ('8', '2', '1'),
  ('9', '2', '1'),
  ('10', '2', '1'),
  ('11', '2', '1'),
  ('12', '2', '1'),
  ('13', '2', '1'),
  ('14', '2', '1'),
  ('15', '2', '1');
✓
UPDATE tablename
SET typ = 3 
WHERE id IN (
  SELECT id 
  FROM (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY idg ORDER BY RANDOM()) rn
    FROM tablename
    WHERE typ = 1
  )
  WHERE rn = 6 -- rn = 6 makes sure that there are at least 6 rows 
); 
✓
SELECT * FROM tablename ORDER BY id;


id
idg
typ


1
1
1

2
1
1

3
1
1

4
1
1

5
1
1

6
1
3

7
1
1

8
2
1

9
2
1

10
2
1

11
2
1

12
2
1

13
2
3

14
2
1

15
2
1

`id`	`idg`	`typ`
`1`	`1`	`1`
`2`	`1`	`1`
`3`	`1`	`1`
`4`	`1`	`1`
`5`	`1`	`1`
`6`	`1`	`3`
`7`	`1`	`1`
`8`	`2`	`1`
`9`	`2`	`1`
`10`	`2`	`1`
`11`	`2`	`1`
`12`	`2`	`1`
`13`	`2`	`3`
`14`	`2`	`1`
`15`	`2`	`1`