MySQL Group By Consecutive Rows

Question

I have a feed application that I am trying to group results from consecutively. My table looks like this:

    postid | posttype | target | action     |              


        

Answer 1

Here's another version that works with MySQL Variables and doesn't require 3 level nesting deep. The first one pre-sorts the records in order by postID and Date and assigns them a sequential number per group whenever any time a value changes in one of the Post ID, Type and/or action. From that, Its a simple group by... no comparing record version T to T2 to T3... what if you wanted 4 or 5 criteria... would you have to nest even more entries?, or just add 2 more @sql variables to the comparison test...

Your call on which is more efficient...

select
      PreQuery.postID,
      PreQuery.PostType,
      PreQuery.Target,
      PreQuery.Action,
      PreQuery.Title,
      min( PreQuery.Date ) as FirstActionDate,
      max( PreQuery.Date ) as LastActionDate,
      count(*) as ActionEntries,
      group_concat( PreQuery.content ) as Content
   from
      ( select
              t.*,
              @lastSeq := if( t.action = @lastAction
                          AND t.postID = @lastPostID
                          AND t.postType = @lastPostType, @lastSeq, @lastSeq +1 ) as ActionSeq,
              @lastAction := t.action,
              @lastPostID := t.postID,
              @lastPostType := t.PostType
           from
              t,
              ( select @lastAction := ' ',
                       @lastPostID := 0,
                       @lastPostType := ' ',
                       @lastSeq := 0 ) sqlVars
           order by
              t.postid,
              t.date ) PreQuery
   group by
      PreQuery.postID,
      PreQuery.ActionSeq,
      PreQuery.PostType,
      PreQuery.Action    

Here's my link to SQLFiddle sample

For the title, you might want to adjust the line...

group_concat( distinct PreQuery.Title ) as Titles,

At least this will give DISTINCT titles concatinated... much tougher to get let without nesting this entire query one more level by having the max query date and other elements to get the one title associated with that max date per all criteria.