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?
Um, all of them?
Yah, but only if you do this:
SELECT min(*) FROM
(
SELECT min(datecol1) FROM table1
UNION ALL
SELECT min(datecol2) FROM table2
UNION ALL
SELECT min(datecol3) FROM table3
) ss;
Otherwise you need the first one, I think, unless you want to rely on
PG's naming conventions for columns, then you could do:
select min(min) from
(
SELECT min(datecol1) FROM table1
UNION ALL
...
)
- John D. Burger
MITRE
