Query with 2 x subqueryPosted by: Jes Ramsing Date: April 29, 2016 06:44AM I have a query that is bugging me. I "just" need the latest recorded values within for a given partid before a certain sessionid SELECT sessionid, varid, val FROM data_i16 WHERE ROW(sessionid, varid)...
Bug #61936 STRAIGHT_JOIN has no effect on query with subquery in FROM clause Submitted: 21 Jul 2011 6:27Modified: 22 Jul 2011 11:23 Reporter: luo longjiu Email Updates: Status: Verified Impact on me: None Category: MySQL Server: OptimizerSeverity: S2 (Serious) Version: 5.1.48, 5.5....
Bug #9021 Query with subquery does not use index in outer query Submitted: 7 Mar 2005 13:23Modified: 26 Mar 2012 19:37 Reporter: Pete French Email Updates: Status: Closed Impact on me: None Category: MySQL Server: OptimizerSeverity: S1 (Critical) Version: 4.1.7, 5.6.4OS: FreeBSD ...
MySQL数据库(22):子查询 sub query,子查询subquery1、基本概念1.1、子查询嵌套查询下层的程序模块,当一个查询是另一个查询的条件时,称之为子查询一条select语句中,嵌入了另一条select语句1.2、主查询主要的查询对象,第一条select语句,确定所获取的数据目标(数据源
在之前“影响MySQL 应用系统性能的相关因素”一章中我们就已经分析过了Query 语句对数据库性能的影响非常大,所以本章将专门针对MySQL 的Query 语句的优化进行相应的分析。 8.1 理解MySQL的Query Optimizer 8.1.1 MySQL Query Optimizer是什么? 在“MySQL 架构组成”一章中的“MySQL 逻辑组成”一节中我们已经了解到,...
在分析如何优化 MySQL Query 之前,我们需要先了解一下 Query 语句优化的基本思路和原则。一般来说,Query 语句的优化思路和原则主要提现在以下几个方面: 1. 优化更需要优化的Query; 2. 定位优化对象的性能瓶颈; 3. 明确的优化目标; 4. 从 Explain 入手; 5. 多使用profile 6. 永远用小结果集驱动大...
In the meantime I realized after running the query in MySql that you can't use it as a subquery with where statement so I changed it around and this is what works when I run directly in my database : Code: SELECT SUBSTRING_INDEX(GROUP_CONCAT(id separator ','), ',', 5) FROM `my...
mysql提供了explain query_sql进行查询分析,下边是一些参数说明: ◆ ID:Query Optimizer 所选定的执行计划中查询的序列号; ◆ Select_type:所使用的查询类型,主要有以下这几种查询类型 ◇ DEPENDENT SUBQUERY:子查询中内层的第一个SELECT,依赖于外部查询的结果集; ...
$subQuery = (newQuery())->select('id')->from('user')->where('status=1');// SELECT * FROM (SELECT `id` FROM `user` WHERE status=1) u$query->from(['u'=> $subQuery]); 前缀 from还可以应用默认的tablePrefix前缀,实现细节请参考“数据库访问对象指南”的“Quoting Tables”章节. ...
Jes Ramsing May 02, 2016 05:32AM Re: Query with 2 x subquery 1051 Rick James May 01, 2016 11:58PM Re: Query with 2 x subquery 1098 Jes Ramsing May 02, 2016 02:16AM Sorry, you can't reply to this topic. It has been closed....