Mysql 插入记录时检查记录是否已经存在，存在则更新，不存在则插入记录SQL

I rarely hesitate to use the above since they are so convenient and provide real performance benefits in many situations. MySQL has other keywords which are more dangerous, however, and should be used sparingly. These includeINSERT DELAYED, which tells MySQL that it is not important to insert the data immediately (say, e.g., in a logging situation). The problem with this is that under high load situations the insert might be delayed indefinitely, causing the insert queue to baloon. You can also give MySQL index hints about which indices to use. MySQL gets it right most of the time and when it doesn‘t it is usually because of a bad scheme or poorly written query.

重要的就是上面提到的 :

INSERT ... SELECT

INSERT ... ON DUPLICATE KEY UPDATE

INSERT ... ON DUPLICATE REPLACE

比如想往表中插入一条数据，如果表中没有该条数据才插入，如果已经存在该条数据就不插入。

首先，在创建表时，将不需要重复的字段设置为unique，然后在插入时，使用insert ignore语句。

例如：（数据库用的是mysql5）
创建一张表用来存储用户：
create table user_info
(
   uid mediumint(10) unsigned NOT NULL auto_increment primary key,
   last_name char(20) not null,
   first_name char(20) not null,
   unique ( last_name, first_name)
);
alter table anser add UNIQUE (last_name,first_name)
插入数据：
insert ignore into user_info (last_name,first_name) values (‘x‘,‘y‘);
这样一来，如果表中已经存在last_name=‘x‘且first_name=‘y‘的数据，就不会插入，如果没有就会插入一条新数据。

上面的是一种用法， 也可以用 INSERT .... SELECT 来实现。

http://blog.csdn.net/langeldep/article/details/6241155

请博主参考 Replace语句
http://dev.mysql.com/doc/refman/5.0/en/replace.html

Mysql 插入记录时检查记录是否已经存在，存在则更新，不存在则插入记录SQL

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