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用例子说明inner join,left join,right join,full join的区别 tisswb.com 28 Dec 2009 | 08:54 pm
最近论坛的数据超过了1600万了，时不时的出现访问速度超慢的情况，虽然不是出现频率很多，但也很影响论坛的正常运行。今天终于抽出一些时间来优化一下，经过分析，发现主要是在一个更新主贴回帖数的语句上出现了问题，因为我们的论坛是从dvbbs转过来的，所以当时这个语句做过调整，原来的语句是 SELECT count(*) FROM cdb_posts AS p LEFT JOIN cdb_members...
Alternativa ao NOT IN com LEFT JOIN Postgres battisti.wordpress.com 25 Apr 2009 | 12:51 pm
Introdução Manipular tabelas via SQL é uma arte, existem diversas formas de fazer a mesma coisa, veja as tabelas abaixo: +------------+ | USUARIO | +------------+ | usr_cod | | usr_login | | pss_co |...
SQL多表连接查询INNER JOIN, LEFT JOIN , RIGHT JOIN ,FULL JOIN ,CROSS JOIN zhangpingyong.com 7 Mar 2012 | 04:40 am
inner join,full outer join,left join,right jion 内部连接 inner join 两表都满足的组合 full outer 全连 两表相同的组合在一起，A表有，B表没有的数据（显示为null）,同样B表有 A表没有的显示为(null) A表 left join B表 左连,以A表为基础，A表的全部数据，B表有的组合。没有的为null A表 r...
SQL LEFT Function sql-statements.com 5 Dec 2011 | 01:03 pm
SQL LEFT() function is used to get left part of a string with the length of specified number. It is supported by MySQL, MS SQL Server, Access, but not by Oracle. SQL LEFT Function Syntax Note: 1, I...
MySQL: Deleting with Left Join dinke.net 15 Dec 2009 | 03:04 pm
Today I had to deal with one huge table and cleanup all data where foreign key doesn’t have it’s primary key match in original table, just to remind myself how sub-queries in MySQL are terrible slower...
Quirk in MySQL Join Conditions nodans.com 25 Oct 2011 | 07:30 am
I found a quirk in a join condition today that caused too many records to display. Look at the following query and notice the two AND clauses after the LEFT JOIN to activitytype. SELECT * FROM organi...
MySQL Left Join mysqldiary.com 6 Jul 2011 | 09:23 pm
Even if you think you know everything about LEFT JOIN, I bet you will learn something or two in this post! A reminder about “A LEFT JOIN B ON conditional_expr” The ON condition (in the expression “A L...
SQL多表连接查询INNER JOIN, LEFT JOIN , RIGHT JOIN ,FULL JOIN ,CROSS JOIN zhangpingyong.com 6 Mar 2012 | 11:40 pm
inner join,full outer join,left join,right jion 内部连接 inner join 两表都满足的组合 full outer 全连 两表相同的组合在一起，A表有，B表没有的数据（显示为null）,同样B表有 阅读全文——共2573字
Comparing EXISTS vs LEFT JOIN WHERE NOT NULL sqlserverplanet.com 27 Dec 2012 | 01:50 am
Two of the most common ways to check for the existence of records is to use a WHERE EXISTS or to perform a LEFT JOIN WHERE values are NOT NULL. My personal choice is usually to use the EXISTS method w...
SQL Tips & Tricks: full-text query optimization mono-software.com 20 Jan 2013 | 05:00 am
How to optimize your slow SQL full text index query that uses a combination of LEFT JOIN and OR operators. A simple switch to the EXISTS operator will make all your performance problems disappear in a...
