MySQL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。
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