分享程序员开发的那些事...
更新时间：2023-01-29 17:22:01
索引中列的顺序是不是无关。有一种方法。
The order of columns in an index is not irrelevant. There is a method.
首先，相等条款中涉及的一个或多个列合并与AND。
First, one or more columns that are involved in equality terms combined with AND.
WHERE a = 1 AND b = 2
其次，参与范围术语的单个列。要么是这样，要么是一个或多个列参与排序。
Second, a single column involved in a range term. Either that, or else one or more columns involved in sorting.
WHERE a = 1 AND b = 2 AND c > 3
或
WHERE a = 1 AND b = 2
ORDER BY c, d
第三，select-list中引用的列，但未通过搜索或排序引用。
Third, columns referenced in the select-list, but which aren't referenced by searching or sorting.
SELECT x, y, z
. . .
WHERE a = 1 AND b = 2 AND c > 3
这将导致（a，b，c，x，y，z）。
我在演讲中更详细地解释了这一点如何设计索引，真的。
I explain this in more detail in my presentation How to Design Indexes, Really.