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MySQL的replace into分析

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Jun 07, 2016 pm 05:12 PM

replace into和insert into是很相似的，唯一的差别就是使用replace into的时候会首先根据表的主键来判断是否存在与将要replace i

replace into和insert into是很相似的，唯一的差别就是使用replace into的时候会首先根据表的主键来判断是否存在与将要replace into的语句相同的记录，如果有的话，就先将旧记录删除，然后在插入新纪录。并且replace into执行后会返回一个数值，如果为1则表示执行的时候插入了一条数据，如果为2表示执行时删除了旧记录并且插入了新纪录。

虽然replace into在平常使用过程中不会出现什么严重的问题。如果我们要操作的表中有一个自增的主键，那么就要出问题了。首先，，因为新纪录与老记录的主键值不同，所以其他表中所有与本表老数据主键id建立的关联全部会被破坏。其次，就是，频繁的REPLACE INTO 会造成新纪录的主键的值迅速增大。总有一天。达到最大值后就会因为数据太大溢出了。就没法再插入新纪录了。数据表满了，不是因为空间不够了，而是因为主键的值没法再增加了。

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