mysql数据库操作记录持续更新...

1.查看删除数据库表的唯一约束

SHOW INDEX FROM tbl_name （唯一约束也是索引）
ALTER TABLE tbl_name DROP INDEX index_name

2.update where中不能使用子查询，解决方案如下：

将子查询作为一张表放在前面

UPDATE `areainfo` a,  (
    SELECT code  FROM `areainfo` where level = 1
) b SET a.`level` =2  WHERE a.`parent_code`  = b.code

UPDATE `areainfo` a,  (
    SELECT code, name  FROM `areainfo` where level = 1
) b SET a.`fullName` =concat(b.name,‘,‘,a.name) WHERE a.`parentCode`  = b.code and a.level = 2

UPDATE `areainfo` a,  (
    SELECT code, name,parentCode  FROM `areainfo` where level = 2
) b , (
    SELECT code, name  FROM `areainfo` where level = 1
) c SET a.`fullName` =concat(c.name,‘,‘,b.name,‘,‘,a.name) WHERE a.`parentCode`  = b.code and b.`parentCode`  = c.code and a.level = 3

原文地址：https://www.cnblogs.com/zarawu/p/10419845.html