MySQL-树型结构数据查询

建表

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for treetest
-- ----------------------------
DROP TABLE IF EXISTS `treetest`;
CREATE TABLE `treetest`  (
  `id` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL COMMENT id,
  `pid` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT 父id,
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT 名字
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of treetest
-- ----------------------------
INSERT INTO `treetest` VALUES (t1, NULL, 根节点);
INSERT INTO `treetest` VALUES (t2, t1, 一级节点A);
INSERT INTO `treetest` VALUES (t3, t1, 一级节点B);
INSERT INTO `treetest` VALUES (t4, t2, 二级节点C);
INSERT INTO `treetest` VALUES (t5, t2, 二级节点D);
INSERT INTO `treetest` VALUES (t6, t3, 二级节点E);
INSERT INTO `treetest` VALUES (t7, t3, 二级节点F);
INSERT INTO `treetest` VALUES (t8, t4, 三级节点G);
INSERT INTO `treetest` VALUES (t9, t8, 四级节点H);
INSERT INTO `treetest` VALUES (tA, NULL, 根节点);
INSERT INTO `treetest` VALUES (tB, tA, 一级节点1);

SET FOREIGN_KEY_CHECKS = 1;

自顶向下

WITH RECURSIVE temp as (
	SELECT t.* FROM treetest t WHERE t.id = tA
	UNION ALL
	SELECT t.* FROM treetest t INNER JOIN temp ON t.pid = temp.id
)
SELECT * FROM temp

自底向上

方法一

WITH RECURSIVE temp as (
	SELECT t.* FROM treetest t WHERE t.id = t9
	UNION ALL
	SELECT t.* FROM treetest t INNER JOIN temp ON t.id = temp.pid
)
SELECT * FROM temp

方法二

SELECT
	* 
FROM
	(
	SELECT
		@r AS oid,
		( SELECT @r := pid FROM treetest WHERE id = oid ) AS pid,
		@l := @l + 1 AS sort 
	FROM
		( SELECT @r := t9, @l := 0 ) vars,
		treetest h 
	) t 
WHERE
	t.oid IS NOT NULL 
ORDER BY
	t.sort ASC

这里加()t这一层是因为最后的@r为Null，条件筛选都是此值，会导致筛选失效