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HomeDatabaseMysql TutorialMySQL查询优化注意下面的四个细节

在任何一个数据库中,查询优化都是不可避免的一个话题。对于数据库工程师来说,优化工作是最有挑战性的工作。MySQL开源数据库也不例外。其实联动北方认为,数据库优化并没有大家所想象的那么苦难。通常情况下,大家可以从以下四个细节出发来做好MySQL数据库

在任何一个数据库中,查询优化都是不可避免的一个话题。对于数据库工程师来说,优化工作是最有挑战性的工作。MySQL开源数据库也不例外。其实联动北方认为,数据库优化并没有大家所想象的那么苦难。通常情况下,大家可以从以下四个细节出发来做好MySQL数据库的查询优化工作。

一、利用EXPLAIN关键字来评估查询语句中的缺陷

笔者在数据库中执行了一条简单的Select查询语句,从一个表格中查询所有信息。现在数据库管理员想知道,数据库在执行这条语句时,做了哪些工作?或者说想知道,这条查询语句有没有进一步优化的可能。如果要了解这个信息的话,就可以在查询语句中加入一个Explain关键字。

二、数据比较时采用相同类型的列以提高查询效率

在数据查询时,有时候会在条件语句中加入判断的条件。如现在有两张表:用户基本信息表和用户权限表,两者通过用户编号作为关联。现在需要查询出每个用户对应什么样的权限,此时就要通过用户编号作为查询条件来进行查询。

三、在Like关键字的起始处通配符要谨慎使用

在实际工作中,笔者发现不少数据库管理员有一个不好的习惯。他们在使用Like等关键字时,通配符会乱用。如现在用户需要查找所有以“LOOK”为前缀的产品信息。用户在查询时,会习惯性的使用下面的语句进行查询:like “%LOOK%”。这个条件语句会查询出所有品名中有LOOK这个单词的纪录,而不是查询出以LOOK为前缀的产品信息。

四、尽量使用其它形式来代替Like关键字

上面提到在使用Like关键字时需要注意通配符的位置。其实从查询效率来看,我们不仅需要注意通配符的位置,而且能够不用Like关键字最好就不用。

参考链接:http://bbs.landingbj.com/t-0-244231-1.html


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