Database optimization

Database optimization

Idea: Optimize the query statement first, then back it up and modify it

1. Try not to use * when querying

2. Query and add an index/foreign key (add the condition item of the query statement directly in navcate)

例：select * from table where age>18 and sex="男"
给age和sex加外键，优先检索前面的age【二叉树最小值】

3. Design reasonable sql query conditions and use and according to the actual situation

4. When using 'or' to query, try not to use "or", try to use "union all"

注：一旦用or就不走索引了，union all 是走索引，先一个表单独查，再做并集

5. Use like fuzzy query (% in the statement)

尽量不要在需要查询的关键字之前加%，因为这样就不走索引了

6. When using count, the most efficient order is count(field name) <count(*) <count(1)

7. In addition to count, average, etc., try not to use the functions that come with sql

因为：自带的函数不走索引

8. Use the sql statement optimization tool: exlain/desc [a set of command tools, you must check the specific usage]

用法：exlain 正常sql语句

9. Database Design Principles

9.1尽量遵循三大范式
    字段类型
        varchar(长度+1) 
            用户名
            描述
            邮箱
            手机号
        char
            手机号
            密码
        int
            性别(int/tinyint) 数字比字符查询速度快
9.2所有字段尽量设计成NotNull
9.3表引擎尽量用Innodb
    Innodb支持事务，MyIsam不支持
    Innodb是行锁，MyIsam是表锁  锁是防止多个sql语相互冲突
    Innodb不支持全文检索，MyIsam支持全文检索

10. For operations with high query frequency, try to use MemCache (third-party database caching tool) and redis (memory database, non-relational database, with its own deduplication)

MemCache 适合不太频繁改变sql语句的查询，位于应用与数据库之间
频繁写入的数据库不适合用关系型数据库，适合用redis - 例：购物车功能、浏览次数统计；注：通常redis和mysql一起使用，redis负责频繁读写的功能

11. Sub-table (consider this last, you need to modify the corresponding query statement)

按列分 - 分离数据项
按行分 - 逻辑分区

12. Multiple libraries, read and write separation

主从设置

13.mysql configuration

14. Hardware configuration

cpu使用率、应用程序所占进程、mysql进程

15: Other

当数据太多时候不要在高峰期添加索引，索引是将字段加到一张索引表，对导致短暂卡顿
时间戳现在是10位或13位(带毫秒)，到2030年失效
业务逻辑尽量不要给数据库处理，在程序中处理，逻辑单边化独立化