MySQL 8.0

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CREATE TABLE vouchers (
  voucherID INT,
  active INT
);
INSERT INTO vouchers VALUES (1, 0), (2, 0), (3, 0), (4, 0), (5, 1), (6, 1);
CREATE TABLE ownsvoucher (
  userID INT,
  voucherID INT
);
INSERT INTO ownsvoucher VALUES
  (44, 5),
  (50, 6),
  (60, NULL),
  (70, NULL);
CREATE TABLE users (
  userID INT
);
INSERT INTO users VALUES (44), (50), (60), (70);
SELECT users.userID, vouchers.voucherID FROM (users, vouchers) LEFT JOIN ownsvoucher ov ON ov.userID = users.userID AND ov.voucherID = vouchers.voucherID 
WHERE vouchers.active = 1 AND ov.voucherID IS NULL
ORDER BY users.userID, vouchers.voucherID


userID
voucherID


44
6

50
5

60
5

60
6

70
5

70
6


INSERT INTO ownsvoucher (userID, voucherID)
  SELECT users.userID, vouchers.voucherID 
  FROM (users, vouchers) 
    LEFT JOIN ownsvoucher ov ON ov.userID = users.userID AND ov.voucherID = vouchers.voucherID 
  WHERE vouchers.active = 1 AND ov.voucherID IS NULL
SELECT * FROM ownsvoucher


userID
voucherID


44
5

50
6

60
null

70
null

44
6

50
5

60
5

60
6

70
5

70
6

userID	voucherID
44	5
50	6
60	null
70	null
44	6
50	5
60	5
60	6
70	5
70	6