MySQL的：去除连续重复值 [英] MySQL: remove consecutive duplicate values

问题描述

我有一个MySQL表返回值的列表，其中包含的连续重复（当时间戳排序）。

I have a MySQL table that returns a list of values that contains consecutive duplicates (when ordered by a timestamp).

例如，查询的时候，我只需要返回连续重复的值：

For example, when querying, I need to only return the consecutively duplicated values:

[1, "Yellow"]
[2, "Yellow"]
[3, "Green"]
[5, "Black"]
[6, "Green"]
[7, "Green"]

这里的数字被用于参考 - 的值实际上字符串绿，因此对于上述情形，新unduped列表将是：

The numbers here are being used for reference - the value is actually the string "Green", so for the above case the new unduped list would be:

[1, "Yellow"]
[3, "Green"]
[5, "Black"]
[6, "Green"]

有没有处理这个问题，MySQL的一个聪明的办法？

Is there a smart way of handling this problem with MySQL?

使用Rails / ActiveRecord的，倒不是说应该有所作为，但我可以做到这一点没有任何问题，由<一个href="http://stackoverflow.com/questions/4576652/how-do-you-merge-consecutive-repeating-elements-in-an-array">manipulating阵列，只是不知道是否有处理这是一个更聪明的方式。

Using Rails/ActiveRecord, not that that should make a difference, but I can do this no problems by manipulating an Array, just wondering if there is a smarter way of handling this.

推荐答案

大厦艾克·沃克的回答，这可能是一个复杂一点比它需要的：

Building on Ike Walker's answer, which is possibly a bit more complex than it needs to be:

set @last='';
select id,@last as last_color,@last:=color as this_color
from your_table
having this_color != last_color;

HAVING ，您可以使用计算列。设置 @Last 意味着它不会从你跑一次查询，这可能会给你奇怪的结果还记得的价值。

HAVING lets you use the computed columns. Setting @last means it won't remember the value from the last query you ran, which might give you strange results.

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