Question

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

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"]

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"]

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

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.

Answer 1

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 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.