MySQL数据库的基本结构与索引的优化方案
以下的文章主要介绍的是MySQL数据库的基本结构，MySQL数据库索引的优化方案与查询语句的优化这些内容。这些相关的内容说对于数据库新手来说可以说意义很大，以下就是文章的具体内容描述。 MySQL数据库结构 字段类型的定义时遵循以下规则: 选用字段长度最小
以下的文章主要介绍的是MySQL数据库的基本结构，MySQL数据库索引的优化方案与查询语句的优化这些内容。这些相关的内容说对于数据库新手来说可以说意义很大，以下就是文章的具体内容描述。
MySQL数据库结构
字段类型的定义时遵循以下规则:
选用字段长度最小
优先使用定长型
尽可能的定义 "NOT NULL"
数值型字段中避免使用 "ZEROFILL"
如果要储存的数据为字符串, 且可能值已知且有限, 优先使用 enum 或 set
MySQL数据库索引的优化
被索引的字段的长度越小, 该索引的效率越高
被索引的字段中, 值的重复越少, 该索引的效率越高
查询语句中, 如果使用了 "group" 子句, 根据其中字段出现的先后顺序建立多字段索引
查询语句中, 如果使用了 "distinct", 根据其中字段出现的先后顺序建立多字段索引
"where" 子句中, 出现对同一表中多个不同字段的 "and" 条件时, 按照字段出现的先后顺序建立多字段索引
"where" 子句中, 出现对同一表中多个不同字段的 "or" 条件时, 对重复值最少的字段建立单字段索引
进行 "内/外连接" 查询时, 对 "连接字段" 建立索引
对 "主键" 的 "unique" 索引 毫无意义, 不要使用
被索引字段尽可能的使用 "NOT NULL" 属性
对写入密集型表, 尽量减少索引, 尤其是 "多字段索引" 和 "unique" 索引
MySQL数据库查询语句的优化
多多利用 "explain" 查询索引使用情况, 以便找出最佳的查询语句写法和索引设置方案
慎用 "select *", 查询时只选出必须字段
查询使用索引时, 所遍历的索引条数越少, 索引字段长度越小, 查询效率越高 (可使用 "explain" 查询索引使用情况)
避免使用 MySQL 函数对查询结果进行处理, 将这些处理交给客户端程序负责
使用 "limit" 时候, 尽量使 "limit" 出的部分位于整个结果集的前部, 这样的查询速度更快, 系统资源开销更低
在 "where" 子句中使用多个字段的 "and" 条件时, 各个字段出现的先后顺序要与多字段索引中的顺序相符
在 "where" 子句 中使用 "like" 时, 只有当通配符不出现在条件的最左端时才会使用索引
在 MySQL 4.1 以上版本中, 避免使用子查询, 尽量使用 "内/外连接" 实现此功能
减少函数的使用, 如果可能的话, 尽量用单纯的表达式来代替
避免在 "where" 子句中, 对不同字段进行 "or" 条件查询, 将其拆分成多个单一字段的查询语句效率更高
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