前言说起SQL调优，不少人认为是个高难度的事情，让人望而却步。但其实在日常的运维过程中，慢SQL却是一个常见的问题，这时大家或多或少会用到一些常用的调优手段，比如加索引、调整执行计划等。接下来，我们将通过三大环节详细讲解如何发现、分析和优化“慢SQL”，具体包括利用慢日志定位问题、分析执行计划并...

问答 2022-02-25 来自：开发者社区

sql 查询语句执行，之后，会有受影响行数， sql 调优，受影响的行数是否越少越好？

比如：下面这个查询语句，受影响 17行，问题1：我通过加索引，等优化 sql的方式，让受影响的行数变小，这样是否可行？问题2：受影响的行数是什么意思？（我连了两次表，where后面有多个限制条件，只有17行受影响？）问题3：受影响的行数，是否可以作为sql 调优的一个指标，比如，我改进后的sql 语句，受影响的行数少，就表示sql语句，进行了优化？请大神解答，感激不尽……

文章 2022-02-16 来自：开发者社区

SQL Server查询性能问题调优案例

这个是朋友让我帮忙看的，一个查询跑的很慢，运行一次要超过1分钟。我看了一下执行计划：这里面两张大表的Join竟然选择了Nested Loop Join(一张表返回170W另外一张返回40W数据).一般Nested Loop Join试用在外部表数据比较小，而内部表又有索引的情况下，性能好。但是这里两张表的数据都很大，这里用Nes...

文章 2022-02-16 来自：开发者社区

作为一个DBA，排除SQL Server问题是我们的职责之一，每个月都有很多人给我们带来各种不能解释却要解决的性能问题。我就多次听到，以前的SQL Server的性能问题都还好且在正常范围内，但现在一切已经改变，SQL Server开始糟糕，疯狂的事情不能解释。在这个情况下我介入，分析下整个SQL Server的安装，最后用一些神奇的调查方法找出性能问题的根源。但很多时候问题的根源是一样的....

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