Re: Does SQL by chance currently support row look-behind and look-ahead?

Good luck! Let us know if it works - or even if it doesn't - it's all
good to know, right?

Vern

On 3/9/2023 8:49 PM, Javier Sanchez wrote:

Great Vern!

I will go ahead and try it out.

Stay well, take care.

Javier.

El jue, 9 mar 2023 a las 19:40, Vern Hamberg via MIDRANGE-L (<
midrange-l@xxxxxxxxxxxxxxxxxx>) escribió:

I googled for "join row with previous row sql" and got this hit -

https://stackoverflow.com/questions/710212/is-there-a-way-to-access-the-previous-row-value-in-a-select-statement

It mentions lag and lead functions - these are OLAP functions - I
wondered if they exist on the i. And they do -

LAG or LEAD Returns an expression value computed using rows prior to or
following the current row.

These seem to have been added in 7.3 - yes, it is not in 7.2

This looks like just the thing - you do need something that sorts the
results - a windowing thing - it's explained in the manual,
https://www.ibm.com/docs/en/ssw_ibm_i_73/pdf/rbafzpdf.pdf, around page
184.

Enjoy!!
Vern

On 3/9/2023 6:36 PM, Javier Sanchez wrote:

I have always liked the idea of doing something with the previous

and/or

the next-look-ahead row while you work with the current row. I suspect
that exists. But not with external coding but with some kind of say:

select col1, col2 + PREVIOUS_ROW(col1) from sometable where
somecondition=true/false; // whatever

There may also be a kind of NEXT_ROW(col2) thing.

This is of course a meta-statement of the idea.

You may say I can write a UDF that returns the previous row col2 value,

but

it would be very difficult because of the nature of your table and your
logic.

It would be nice that this be an intrinsic DB2 functionality. Do we

have

that already?

Please your comments.

TIA.

Javier.

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