数据索引的设计，都和什么有关？
先找出执行频率最高的sql，然后找出量比较大的表，然后把就是结合查询计划去实现这些语句的 索引 覆盖，还是sqlserver强大，查询计划是图形化的，mysql得explan有些弱呀。 1.作为where、join字段在生产环境下的使用频率，注意 索引 在哪些情况下不被使用 2.
先找出执行频率最高的sql，然后找出量比较大的表，然后把就是结合查询计划去实现这些语句的索引覆盖，还是sqlserver强大，查询计划是图形化的，mysql得explan有些弱呀。
1.作为where、join字段在生产环境下的使用频率，注意索引在哪些情况下不被使用 2.大数据表要做到CURD性能综合平衡：充分考虑索引对CUD的影响 3.OLTP和OLAP：用时间和空间来减少即需查询 4.需要使用唯一索引来保证数据的业务约束。5.原则索引应尽量使用数值字段 6.聚集索引和非聚集索引：最频字段或主键。7. 索引无法解决的问题要通过OLAP、(分布式)缓存等解决。索引对硬盘的伤害，即索引会增加写硬盘，写对硬盘的伤害比读大。
1:和数据操作方式有关，简单说就是SQL怎么写，查询条件和更新条件；2:和数据操作频次有关，读频率高和写频率高，处理思路会有不同；3:和数据容量有关；4:和数据分布特征有关；特别是复合索引设计，需呀理解数值分布的均匀度和散列特征；
索引本身带来的代价(变更频度,索引维护单次开销,索引空间,并发开销), 索引带来的好处(查询的开销变化, 查询的频度), 这两者的交叉点, 就是选择使用/不使用新的索引的交叉点
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