Question

How I can to group continuous data in MySQL table and store its number to an extra column?

For example:

id, n

1   10
2   10
3   10
4   56
5   10
6   10
7   80
8   12

I want to get something like this. Notice that n of 10 is listed twice.

id   n   cnt
 1   10   3
 4   56   1
 5   10   2
 7   80   1
 8   12   1

Is that any way to do this without FUNCTION?

Answer 1

You can with use of MySQL Variables

select
      min( PreQuery.ID ) as StartIDOfGroup,
      PreQuery.n,
      count(*) as Cnt
   from
      ( select yt.id,
               yt.n,
               @CommonGroup := @CommonGroup + if( @LastNValue = yt.n, 0, 1 ) as Common,
               @LastNValue := yt.n as JustAPlaceholder
           from
              YourTable yt,
              ( select @CommonGroup := 0, @LastNValue := 0 ) SQLVars ) PreQuery
   group by
      PreQuery.n,
      PreQuery.Common
   order by
      StartIDOfGroup