[oldboy_c64 ~]# mysql --help|grep dummy        -U, --i-am-a-dummy Synonym for option --safe-updates, -U.i-am-a-dummy      FALSE

在mysql命令加上选项-U后，当发出没有WHERE或LIMIT关键字的UPDATE或DELETE时，mysql程序就会拒绝执行

[oldboy_c64 ~]# mysql -uroot -poldboy123 -S /data/3306/mysql.sock -UWelcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 14Server version: 5.5.32-log MySQL Community Server (GPL)Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> delete from oldboy.student; ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY columnmysql> quitBye

提示：不加条件无法删除，目的达到。

[oldboy_c64 ~]# alias mysql='mysql -U'[oldboy_c64 ~]# mysql -uroot -poldboy123 -S /data/3306/mysql.sockWelcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 15Server version: 5.5.32-log MySQL Community Server (GPL)Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> delete from oldboy.student; ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY columnmysql> delete from oldboy.student where Sno=5;Query OK, 1 row affected (0.02 sec)mysql> quitBye[oldboy_c64 ~]# echo "alias mysql='mysql -U'" >>/etc/profile[oldboy_c64 ~]# . /etc/profile[oldboy_c64 ~]# tail -1 /etc/profilealias mysql='mysql -U'

结论：