Re: How to write such a query

On 9/18/20 3:18 PM, Igor Korot wrote:
> Hi, Ken,
>
> On Fri, Sep 18, 2020 at 2:46 PM Ken Tanzer <ken(dot)tanzer(at)gmail(dot)com
> <mailto:ken(dot)tanzer(at)gmail(dot)com>> wrote:
>
> > How to find what the primary key (or UNIQUE identifier) value is
> > for row 5 in the recordset?
>
> You're missing the point: as mentioned before, there is no "row
> 5". To
> update the 5th record that you've fetched, you increment a counter
> each time
> you fetch a row, and when you read #5, do an UPDATE X SET field1 =
> 'blarg'
> WHERE id = <thekeyvalue>;
>
>
> It seems worth mentioning for benefit of the OPs question that there
> _is_ a way to get a row number within a result set.  Understanding and
> making good use of that is an additional matter.
>
> SELECT X.field1, Y.field2*,row_number() OVER ()* from X, Y WHERE X.id
> = Y.id -- ORDER BY ____?
>
> That row number is going to depend on the order of the query, so it
> might or might not have any meaning. But if you queried with a primary
> key and a row number, you could then tie the two together and make an
> update based on that.
>
>
> Thank you for the info.
> My problem is that I want to emulate Access behavior.
>
> As I said - Access does it without changing the query internally (I presume).
>
> I want to do the same with PostgreSQL.
>
> I'm just trying to understand how to make it work for any query
>
> I can have 3,4,5 tables, query them and then update the Nth record in the
> resulting recordset.
>
> Access does it, PowerBuilder does it.
>
> I just want to understand how.

They do it by hiding the details from you.

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