Re: NEWBIE: How do I get the oldest date contained in 3 tables

On 4/9/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Dann Corbit" <DCorbit(at)connx(dot)com> writes:
> >> owner(at)postgresql(dot)org] On Behalf Of Lorenzo Thurman
> >> I have three tables using date fields. I want to retrieve the oldest
> >> date contained in the tables. Can someone show me an example of a query
> >> that would do that?
>
> > Just do a union and return the min
>
> That's probably not enough detail for a newbie ...
>
> SELECT min(x) FROM
> (
> SELECT min(datecol1) AS x FROM table1
> UNION ALL
> SELECT min(datecol2) AS x FROM table2
> UNION ALL
> SELECT min(datecol3) AS x FROM table3
> ) ss;
>
> Exercise for newbie: which of the AS clauses are redundant?

they are all unnecessary :D

select least
(
(SELECT min(datecol1) FROM table1),
(SELECT min(datecol2) FROM table2),
(SELECT min(datecol3) FROM table3)
);

merlin