sql优化索引使用

Oracle SQL优化之使用索引提示一例

改SQL中还是用了 in 这个关键字，在查询中最好将in使用exists替代来提高性能修改后的sql如下：在看一下执行计划：这个时候解决了mailsend表的全表扫描情况，但是person表最外层还是走的全表扫描（虽然内层走的是主键索引扫描）这才是很...

有关sql语句使用索引优化的问题

现在要对数据库中的数据进行统计,统计最近一个月的数据,现数据库的设计中有3个跟时间有关的...使用concat函数后索引将失效,这个SQL该如何优化才能够让其执行索引查询.sql如下:这个sql该如何优化才能让你索引生效,使用索引策略查询呢?求指点

SQL优化中索引列使用函数之灵异事件

SQL优化中索引列使用函数之灵异事件在SQL优化内容中有一种说法说的是避免在索引列上使用函数、运算等操作，否则Oracle优化器将不使用索引而使用全表扫描，但是也有一些例外的情况，今天我们就来看看该灵异事件。一般而言，以下情况都会使...

SQL优化中索引列使用函数之灵异事件

在SQL优化内容中有一种说法说的是避免在索引列上使用函数、运算等操作，否则Oracle优化器将不使用索引而使用全表扫描，但是也有一些例外的情况，今天我们就来看看该灵异事件。一般而言，以下情况都会使Oracle的优化器走全表扫描，举例:1....

mysql索引的使用和优化

组合索引（最左前缀）平时用的SQL查询语句一般都有比较多的限制条件，所以为了进一步榨取MySQL的效率，就要考虑建立组合索引。使用组合索引时注意最左匹配原则。比如新建索引ALTER TABLE testADD INDEX 'id_name_age'('id','name','age')。...

postgresql 优化之-不会使用索引

且有组合索引 btree(session_id,session_line_num)，但由于t1.session_line_num=t2.session_line_num+1 至使t2最多只能使用一部分索引-修改条件 t1.session_line_num=t2.session_line_num+1 为t1.session_line_num-1=t2.session_line_num，...

postgresql 优化 order by 对索引使用的影响

((customer_id):text='53a3bfa545cebf2700d727e3':text)在上面的sql中由于ORDER BY create_date DESC的原因，pg使用了idx_create_date索引，但其并不是最有效的，请问pg为什么会使用那个索引，而不使用 idx_customer_id这个索引（其更高效...

【自主研发-贡献给SQL Server人员】索引诊断与优化软件使用说明（1）-总体预览

【自主研发】索引诊断与优化软件使用说明（2）-软件下载，安装【自主研发】索引诊断与优化软件使用说明（3）-软件的功能模块介绍本文转自yanyangtian51CTO博客，原文链接：http://blog.51cto.com/yanyangtian/1075112，如需转载请自行联系...

SQL性能优化中，where语句使用 IN 到底走不走索引？

SQL优化-问题，如何定位及优化SQL语句的性能问题？创建的索引有没有被使用到?或者说...

如何定位及优化SQL语句的性能问题？创建的索引有没有被使用到?或者说怎么才可以知道这条语句运行很慢的原因？

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云数据库RDS SQL Server版

云数据库SQL Server，具有企业许可授权，权限更为开放，引擎功能更为强大。能完美支持Windows平台的.NET架构，支持复杂SQL查询，性能优秀，并有强大的可视化管理工具，帮助您轻松管理数据。

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