create table uni(id int,num char(10) default rand())
insert into uni(id) values(1)
insert into uni(id) values(1)
insert into uni(id) values(1)
insert into uni(id) values(2)
insert into uni(id) values(2)
insert into uni(id) values(3)
insert into uni(id) values(3)
现在创建了一个id重复的表
create table uni2(id int,num char(10))
create unique index removemul on uni2(id)
with ignore_dup_key
insert uni2 select * from uni
这时表uni2中的记录是不重复的
如果要去除两个列的重复值，可同时为两个列建立ignore_dup_key索引
