If your concern is speed, the thing here is that you will have as many records
as there are in "mytable", most of them (I think) with NULLs for alias1, alias2,
alias3 and alias4. This way, there is no condition to filter any record, so
postgreSQL will do a sequential scan over the whole table.
If you are ok fetching the records that match and assumming that the all the others
don't match, then the following will work:
--column1=column2
SELECT column3 AS alias1, column4 AS alias2, column5 AS alias3, NULL AS alias4
FROM myTable
WHERE column1=column2
UNION
--column6=column7
SELECT NULL AS alias1, NULL AS alias2, NULL AS alias3, column8 AS alias4
FROM myTable
WHERE column6=column7
Of course, you will need the necesary indexes.
If this didn't give you a hint, please post a message with a link to your original
message, so I can get a better idea of what you need.
On Friday 30 May 2003 12:47, C F wrote:
> Hello,
> I already tried this same basic question with no response.... maybe I was
> too wordy. So here it is simplified.... what's the best way to write this
> query? I'm open to using stored procedures, but even then I don't know how
> I would conditionally populate a resultset (refcursor). Notice that in the
> first three cases, the expression is the exact same, only the return value
> is different. This seems inefficient....
>
>
> select
> (case when column1 = column2 then column3 end) as alias1,
> (case when column1 = column2 then column4 end) as alias2,
> (case when column1 = column2 then column5 end) as alias3,
> (case when column6 = column7 then column8 end) as alias4
> from
> mytable
> ;
>
> Any ideas?
> Thanks!
>
>
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