On Tue, Oct 22, 2013 at 10:01 AM, Elliot <yields.falsehood@gmail.com> wrote:
> On 2013-10-21 20:38, Robert James wrote:
>>
>> I have a table of event_id, event_time. Many times, several events
>> happen in a row. I'd like a query which replaces all of those events
>> with a single record, showing the count.
>>
>> Eg: Take A,A,A,B,C,A,D,A,A,D,D,B,C,C and return: A,3; B,1; C,1; A,1;
>> D,1; A,2; D,2; B,1; C,2
>>
>> How can I do that?
>>
>>
>
> It looks like you already found a solution, but here's one with a CTE. I
> cobbled this together from an older query I had for doing something similar,
> for which I unfortunately lost the original source of this approach. Also,
> this implies that there is something that gives an ordering to these rows
> (in this case, the field "i").
>
> create temp table data (i int, val char);
>
> insert into data (val, i)
> values
> ('A',1),
> ('A',2),
> ('A',3),
> ('B',4),
> ('C',5),
> ('A',6),
> ('D',7),
> ('A',8),
> ('A',9),
> ('D',10),
> ('D',11),
> ('B',12),
> ('C',13),
> ('C',14)
> ;
>
> with x
> as
> (
> select i,
> row_number() over () as xxx,
> val,
> row_number() over (partition by val order by i asc)
> - row_number() over () as d
> from data
> order by i
> )
> select val,
> count(*)
> from x
> group by d,
> val
> order by min(i)
wow, that's really clever.
merlin