MySQL优化GROUP BY－松散索引扫描与紧凑索引扫描
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1、MySQL如何优化GROUP BY?http://www.iteedu.com//database/mysql/mysqlmanualcn/optimization/group-by-optimization.php
2、详解MySQL分组查询Group By实现原理?http://www.51testing.com/html/52/n-229952.html
3、松散的索引扫描(Loose index scan)?http://www.coder4.com/archives/1344
4、MySQL学习笔记?http://leeon.me/a/mysql-notes-2
