MySQL安全更新之safe_updates介绍说明
鲍建业
对于研发而言，线上数据库update和delete是非常频繁的，因而经常出现update和delete时，后面忘记添加where条件的限制，导致整个表误删除，或者是误更新，造成很多灾难是非常常见的事情，如何彻底解决这样的人为的数据库故障或者减少这种人为的故障了，那就是从根本上控制好mysql数据库的权限，禁止给研发人员update和delete数据库的权限，严格SQL语句上线之前的审核，减少人为的操作mysql库的故障。然而这种数据库的权限的把控往往是很难严格意义上把控好的。只能是减少类似这样的故障的发生。
下面咱们简单介绍下client端mysql的safe_updates 参数的使用，它从一定程度上还是可以避免上面的update和delete时，后面忘记添加where条件而带来的悲剧。
sql_safe_updates具体的使用方法咱们可以man 下mysql
man mysql|grep sql_safe_updates
SET sql_safe_updates=1, sql_select_limit=1000, max_join_size=1000000;同时也可以把参数写入到/etc/my.cnf配置文件
在my.cnf配置文件开启参数safe-updates就行。
[root@app1 logs]# grep -B 5 safe-updates /etc/my.cnf
[mysql]
auto-rehash
prompt="\\u@\\h [\\d]>"
#pager="less -i -n -S"
#tee=/opt/mysql/query.log
safe-updates查看当前mysql session会话下的sql_safe_updates
root@localhost [(none)]>select @@sql_safe_updates;
+--------------------+
| @@sql_safe_updates |
+--------------------+
| 0 |
+--------------------+
1 row in set (0.00 sec)查看全局的配置参数sql_safe_updates
root@localhost [(none)]>select @@global.sql_safe_updates;
+---------------------------+
| @@global.sql_safe_updates |
+---------------------------+
| 0 |
+---------------------------+
1 row in set (0.00 sec)创建测试表并且插入数据测试
CREATE TABLE `zx_scores` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`titles` char(15) NOT NULL,
`icon` smallint(6) unsigned DEFAULT '0',
`integral` int(10) NOT NULL DEFAULT '0',
`isdefault` tinyint(1) unsigned NOT NULL DEFAULT '0',
`create_time` varchar(20) COLLATE utf8_unicode_ci NOT NULL,
`day` date NOT NULL DEFAULT '0000-00-00' COMMENT '日期',
PRIMARY KEY (`id`),
KEY `integral` (`integral`)
) ENGINE=Innodb AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;给表zx_sorces中的字段titles字段添加一个索引A
root@localhost [test02]>create index A on zx_scores(titles);
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0查看该表存在的索引
root@localhost [test02]>show index from zx_scores;
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| zx_scores | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| zx_scores | 1 | integral | 1 | integral | A | 0 | NULL | NULL | | BTREE | | |
| zx_scores | 1 | A | 1 | titles | A | 0 | NULL | NULL | | BTREE | | |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)通过查看表结构也是可以看到索引的
root@localhost [test02]>desc zx_scores;
+-------------+----------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+----------------------+------+-----+------------+----------------+
| id | int(11) unsigned | NO | PRI | NULL | auto_increment |
| titles | char(15) | NO | MUL | NULL | |
| icon | smallint(6) unsigned | YES | | 0 | |
| integral | int(10) | NO | MUL | 0 | |
| isdefault | tinyint(1) unsigned | NO | | 0 | |
| create_time | varchar(20) | NO | | NULL | |
| day | date | NO | | 0000-00-00 | |
+-------------+----------------------+------+-----+------------+----------------+
7 rows in set (0.00 sec)查看当前sql的模式，0代表sql没有开启安全模式，1代表sql开启了安全模式
root@localhost [test02]>select @@SQL_SAFE_UPDATES;
+--------------------+
| @@SQL_SAFE_UPDATES |
+--------------------+
| 0 |
+--------------------+
1 row in set (0.00 sec)设置sql为安全模式：
root@localhost [test02]>set global sql_safe_updates=1;
Query OK, 0 rows affected (0.00 sec)退出当前的MySQL的session会话层，重新登录mysql查看当前的sql_safe_updates为1，代表开启了sql的安全模式
root@localhost [test02]>select @@SQL_SAFE_UPDATES;
+--------------------+
| @@SQL_SAFE_UPDATES |
+--------------------+
| 1 |
+--------------------+
1 row in set (0.00 sec)给表中插入测试数据：
insert into zx_scores values(1,'列兵',1,0,1,now(),curdate());
insert into zx_scores values(2,'班长',2,1000,1,now(),curdate());
insert into zx_scores values(3,'少尉',3,2000,1,now(),curdate());
insert into zx_scores values(4,'中尉',4,3000,1,now(),curdate());
insert into zx_scores values(5,'上尉',5,4000,1,now(),curdate());
insert into zx_scores values(6,'少校',6,5000,1,now(),curdate());
insert into zx_scores values(7,'中校',7,6000,1,now(),curdate());
insert into zx_scores values(8,'上校',8,7000,1,now(),curdate());
insert into zx_scores values(9,'少将',9,12000,1,now(),curdate());
insert into zx_scores values(10,'中将',10,17000,1,now(),curdate());
insert into zx_scores values(11,'上将',11,22000,1,now(),curdate());
insert into zx_scores values(12,'大将',12,27000,1,now(),curdate());演示一：
root@localhost [test02]>update zx_scores set titles='班长' where icon=1;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>简单翻译一下：你正在使用 安全更新模式（safe upate mode）并且你在尝试 update 一个表时 没有用带有键的列 作为where条件。
初学者在修改一个值时可能会用以下语句：
update table_name set column='new_value'
而这正是很多人常犯的错误。因为他没有限定条件，会将表中所有的记录都修改一遍。
为了防止这种错误出现，我们可以开启安全更新模式（safe update mode）：
set [global] SQL_SAFE_UPDATES = 1;
在update操作中：
1.当update table 时，后面没有where条件，是会拒绝更新的。
root@localhost [test02]>update zx_scores set titles='班长' ;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>2.当where条件中列（column）没有索引可用且无limit限制时会拒绝更新。
root@localhost [test02]>update zx_scores set titles='班长' where icon=1;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>一旦加上limit限制是可以更新的：
root@localhost [test02]>update zx_scores set titles='班长' where icon=1 limit 1;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1 Changed: 1 Warnings: 03.当where条件为常量且无limit限制时会拒绝更新。
root@localhost [test02]>update zx_scores set integral='1000' where 1=1;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>例如：update zx_scores set titles='班长' where icon=1;是会拒绝跟新的
一旦加上limit限制是可以更新的：
root@localhost [test02]>update zx_scores set integral='1000' where icon=1 limit 1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0当where条件为常量且有limit限制时是可以更新的：
root@localhost [test02]>update zx_scores set titles='少将' where 1=1 limit 2;
Query OK, 1 row affected (0.10 sec)
Rows matched: 2 Changed: 1 Warnings: 0在delete操作中：
1.当①where条件为常量，且无limit限制时拒绝删除。
root@localhost [test02]>delete from zx_scores where 1=1;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>当①where条件为常量，且有limit限制是可以删除的。
root@localhost [test02]>delete from zx_scores where 1=1 limit 5;
Query OK, 5 rows affected (0.06 sec)2.当②或where条件为空，且无limit限制时拒绝删除。
root@localhost [test02]>delete from zx_scores;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>3.当③或where条件中 列（column）没有索引可用且无limit限制时拒绝删除。
root@localhost [test02]>delete from zx_scores where icon =1;
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column.
root@localhost [test02]>但是titles字段上创建了索引A,所以可以删除
root@localhost [test02]>delete from zx_scores where titles='班长';
Query OK, 2 rows affected (0.03 sec)
root@localhost [test02]>需要注意的是：
update操作中，where可以为常量 ，where条件中列（column）可以没有索引，但是需要有limit限制。
然而delete要严格一些：where不能为常量，且where条件中列（column）不能没有索引！
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