如何使用另一种方法实现mysql的左连接？

Question

Because MySQL Left join limited 61, maybe this is table:

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for test
-- ----------------------------
DROP TABLE IF EXISTS `test`;
CREATE TABLE `test` (
  `id` int(11) DEFAULT NULL,
  `pid` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

-- ----------------------------
-- Records of test
-- ----------------------------
BEGIN;
INSERT INTO `test` VALUES (1, 3);
INSERT INTO `test` VALUES (1, 4);
INSERT INTO `test` VALUES (2, 4);
INSERT INTO `test` VALUES (3, 5);
INSERT INTO `test` VALUES (3, 6);
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

This is MySQL SQL:

    SELECT
    t1.pid AS lev1,
    t2.pid AS lev2,
    t3.pid AS lev3,
    t4.pid AS lev4

FROM
    test AS t1
    LEFT JOIN test AS t2 ON ( t2.id = t1.pid )
    LEFT JOIN test AS t3 ON ( t3.id = t2.pid )
    LEFT JOIN test AS t4 ON ( t4.id = t3.pid )
    LEFT JOIN test AS t5 ON ( t5.id = t4.pid ) 
WHERE t1.id = 1 ;

I want to output like this but not using MYSQL LEFT JOIN:

lev1,lev2,lev3,lev4
 3,   6,
 3,   5,
 4,    ,

If python can achieve, I also need!

Answer 1

The limit of 61 is there for a reason and your query might run somewhat slowly, but something like the following should work for your needs:

SELECT 
    t1.id AS lev1, t2.id AS lev2, t3.id AS lev3, t4.id AS lev4
FROM
    t1, t2, t3, t4
WHERE
    t2.pid = t1.id AND t3.pid = t1.id AND t4.pid = t1.id