MySQL父查询子、子查询父

一、根据父查询子

1、sql实现

SELECT GROUP_CONCAT(id) id FROM (
		SELECT t1.*,IF(FIND_IN_SET(parentid, @pids) > 0, @pids := CONCAT(@pids, ',', id), '0') AS ischild
		FROM (SELECT * FROM test ORDER BY id ASC) t1,(SELECT @pids := '变量父ID') t2
) t3 WHERE ischild != '0'

需修改的变量：id：主键id、parentid：父id、test：表名。

2、函数实现

2.1、创建函数

CREATE DEFINER=`bd_db_admin`@`%` FUNCTION `getChildId`(`pId` bigint) RETURNS varchar(4000) CHARSET utf8
BEGIN
	#Routine body goes here...
	DECLARE ids VARCHAR(4000);
	DECLARE childId VARCHAR(4000);

	SET ids = '$';
	SET childId = CAST(pId AS CHAR);
	
	WHILE childId is NOT NULL DO
	SET ids = CONCAT(ids,',',childId);
	select GROUP_CONCAT(id) INTO childId FROM test WHERE FIND_IN_SET(parentid,childId)>0;
	END WHILE;

	RETURN ids;
END

2.2、使用

select getChildId(122)

二、根据子id查询父id

SELECT t2.* FROM ( 
    SELECT @r AS _id,  (SELECT @r := parentid FROM test WHERE id = _id) AS parentid, @l := @l + 1 AS lvl 
    FROM (
			SELECT @r := '要查询的ID', @l := 0) vars, test
    WHERE @r <> 0
) t1 JOIN test t2 ON t1._id = t2.id 
ORDER BY t1.lvl DESC

需修改的变量： id：主键、parentid：父id、test：表名。

 

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