-- FIND_IN_SET(id,str)可以查询出str字符串包含的id集合
SELECT * FROM region where FIND_IN_SET(id,'340100,340200')>0; 
-- GROUP_CONCAT(id)把所有查询的id形成一个字符串：id1,id2,id3...
SELECT GROUP_CONCAT(id) FROM region where FIND_IN_SET(pid,'340100')>0;

-- 创建函数方便调用，实现传入一个父id查询所有子集区域
-- 思路：通过id查询他的子id集合，循环查询所有子id的子id，直到子id为空
CREATE  PROCEDURE `getRegionByPid`(
    IN regionId int(11))
BEGIN
	DECLARE pIds VARCHAR(4000);
	DECLARE childIds VARCHAR(4000);
	-- 存放所有父id: id1,id2,id3...
	SET pIds = '';
	-- 存放每次查询来的子id集合: id1,id2,id3...
	SET childIds = CAST(regionId AS CHAR);
	-- 循环查询 
	WHILE childIds is not NULL
	DO
	SET pIds = CONCAT(pIds,',',childIds);
	-- 查询childIds的子id集合
	SELECT GROUP_CONCAT(id) INTO childIds FROM region WHERE FIND_IN_SET(pid,childIds) > 0 ;

	END WHILE;
	-- 查询所有子集
	SELECT * FROM region WHERE FIND_IN_SET(id,pIds);
END
-- 直接调用就可以了
CALL getRegionByPid(340200);

省市区sql脚本

https://blog.csdn.net/qq_42145865/article/details/116899036