mysql记录

group_count函数

group_count做字符串拼接时，默认长度1024字节
查看group_concat_max_len长度
show variables like ‘group_concat_max_len’
解决办法一（重启数据库后失效）：
SET GLOBAL group_concat_max_len=102400;
SET SESSION group_concat_max_len=102400;
解决办法二（重启数据库后生效）：
配置文件添加group_concat_max_len = 102400；

根据子节点查询最上级父节点id

SELECT T2.id, T2.name
FROM (
SELECT
@r AS _id,
(SELECT @r := parent_id FROM unit WHERE id = _id) AS parent_id,
@l := @l + 1 AS lvl
FROM
(SELECT @r := (select p.unit_id from user us left join person p on us.id = p.id where us.id=124), @l := 0) vars, – 查询id为5的所有上级
unit h
WHERE @r <> 0) T1
JOIN unit T2
ON T1._id = T2.id
ORDER BY T1.lvl DESC limit 1;