SQL Question

[Michel Esber]

Hello,

DB2 V8 LUW.

I have a simple table A with fields ID and SESSION_NUMBER (integer).
One ID can have multiple session numbers.

For a given ID, I can find the last two sessions with a simple SQL:

select * from table where ID='xyz' order by SESSION_NUMBER desc fetch
first two rows only

This may be rather simple, but I am stuck:

How do I return only the last two sessions for each ID that this table
has?

TIA, Michel

[mikelbell2000]

Re: SQL Question

Just did something similar. Look up the OLAP rownumber() function.
Partition by your ID field and order by your SESSION_NUMBER
descending. Feed the results of this to an outer query and look for
rows having a rownumber of 2 or less. Something like:

select id, session_number
from (
select id, session_number, rownumber() over (partition by id order
by sess desc) as rn
from table_A
) as tt
where tt.rn <=2


HTH,
Mike


On Feb 15, 2:23 pm, "Michel Esber" <mic...@us.auto matos.comwrote:

Hello,
>
DB2 V8 LUW.
>
I have a simple table A with fields ID and SESSION_NUMBER (integer).
One ID can have multiple session numbers.
>
For a given ID, I can find the last two sessions with a simple SQL:
>
select * from table where ID='xyz' order by SESSION_NUMBER desc fetch
first two rows only
>
This may be rather simple, but I am stuck:
>
How do I return only the last two sessions for each ID that this table
has?
>
TIA, Michel

[Mark A]

Re: SQL Question

On Feb 15, 12:23 pm, "Michel Esber" <mic...@us.auto matos.comwrote:

Hello,
>
DB2 V8 LUW.
>
I have a simple table A with fields ID and SESSION_NUMBER (integer).
One ID can have multiple session numbers.
>
For a given ID, I can find the last two sessions with a simple SQL:
>
select * from table where ID='xyz' order by SESSION_NUMBER desc fetch
first two rows only
>
This may be rather simple, but I am stuck:
>
How do I return only the last two sessions for each ID that this table
has?
>
TIA, Michel

select * from table a
where SESSION_NUMBER in
(select b.SESSION_NUMBE R from table b
where b.ID = a.ID
order by b.SESSION_NUMBE R desc
fetch first 2 rows only)

[Brian Tkatch]

Re: SQL Question

On 15 Feb 2007 11:23:05 -0800, "Michel Esber"
<michel@us.auto matos.comwrote:

>Hello,
>
>DB2 V8 LUW.
>
>I have a simple table A with fields ID and SESSION_NUMBER (integer).
>One ID can have multiple session numbers.
>
>For a given ID, I can find the last two sessions with a simple SQL:
>
>select * from table where ID='xyz' order by SESSION_NUMBER desc fetch
>first two rows only
>
>This may be rather simple, but I am stuck:
>
>How do I return only the last two sessions for each ID that this table
>has?
>
>TIA, Michel

By adding a DATE COLUMN, then use ORDER BY. Without an ORDER BY in the
query, there is no real order, and the results may change in between
executions.

B.

[Mark A]

Re: SQL Question

On Feb 16, 8:04 am, Brian Tkatch <N/Awrote:

>
By adding a DATE COLUMN, then use ORDER BY. Without an ORDER BY in the
query, there is no real order, and the results may change in between
executions.

I think it is reasonable to assume that the SESSION_NUMBER is assigned
sequentially for each ID, and the two highest values are the last two
inserted for a given ID.