Question

I’m using MS SQL Server 2008, and I would like this:

+------+--------+--------+------------+
| id   | Name   | Event  | Timestamp  |
+------+--------+--------+------------+
|    0 | bob    | note   | 14:20      |
|    1 | bob    | time   | 14:22      |
|    2 | bob    | time   | 14:40      |
|    3 | bob    | time   | 14:45      |
|    4 | bob    | send   | 14:48      |
|    5 | bob    | time   | 15:30      |
|    6 | bob    | note   | 15:35      |
|    7 | bob    | note   | 18:00      |
+------+--------+--------+------------+

To become this:

+------+--------+--------+------------+
| id   | Name   | Event  | Timestamp  |
+------+--------+--------+------------+
|    0 | bob    | note   | 14:20      |
|    1 | bob    | time   | 14:22      |
|    4 | bob    | send   | 14:48      |
|    5 | bob    | time   | 15:30      |
|    6 | bob    | note   | 15:35      |
+------+--------+--------+------------+

I.e., rows are “grouped” by the “event” column. Only one of each grouped identical “event” is to be shown.

• If one event, e.g. “note” as with id 0, is in the table with no row directly before or after it (row with nearest timestamps) that has an equal “event” value, it is shown;
• If more than one row with the same event, e.g. “time” as with id 1-3. comes after each others (i.e. no row with a different “event” has a timestamp that is “between” them), any one of them is shown (doesn’t matter for me, all other columns are identical anyway).

Those two are the only rules.

Answer 1

If ids are one after one try do it this way:

select * into #tab from(
    select 0 as id, 'bob' as name, 'note' as event, '14:20' as time union
    select 1, 'bob', 'time', '14:22' union
    select 2, 'bob', 'time', '14:40' union
    select 3, 'bob', 'time', '14:45' union
    select 4, 'bob', 'send', '14:48' union
    select 5, 'bob', 'time', '15:30' union
    select 6, 'bob', 'note', '15:35' union
    select 7, 'bob', 'note', '18:00'
) t

select t.*
from #tab t
left join #tab t1 on t.id = t1.id + 1 and t1.event = t.event 
    -- and t1.name = t.name -- if there are more names you are going to need this one as well
where t1.id is null

result:

id  name    event   time
0   bob     note    14:20
1   bob     time    14:22
4   bob     send    14:48
5   bob     time    15:30
6   bob     note    15:35

Added:

If ids aren’t one after one, you can make them to be:

select identity(int, 1, 1) as id, name, event, time 
into #tab_ordered_ids
from #tab order by name, id, time