set sql_safe_updates = 1;

CREATE TABLE working.test01 (id INT NOT NULL AUTO_INCREMENT,NAME VARCHAR(20),age INT,gmt_created DATETIME,PRIMARY KEY(id));

 insert into test01(name,age,gmt_created) values('xiaowang',2,now());
 insert into test01(name,age,gmt_created) values('huahua',5,now()); 
 insert into test01(name,age,gmt_created) values('gougou',9,now()); 
 insert into test01(name,age,gmt_created) values('heihei',12,now()); 
 insert into test01(name,age,gmt_created) values('baibai',134,now()); 

# 过滤字段上没有索引
update
update test01 set name = 'xiaoxiao' where age = 2 ；
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
# 全表更新
update test01 set name = 'xiaoxiao';
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
# 加入limit的更新
update test01 set name = 'xia' limit 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

# 新增索引
create index idx_age on test01(age);

update test01 set name = 'xiaoxiao' where age = 2;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0

update test01 set name = 'hhh' where age = 9 limit 10;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

alter table test01 drop index idx_age;
create index idx_age_name on test01(age,name);


update test01 set age= 100 where name = 'hhh';
ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column

update test01 set age= 100 where name = 'hhh' limit 10;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

update t1 set col2=1 where key1 in (select col2 from t2 where key2='ABcD');

ERROR 1175 (HY000): You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column