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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...

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