Re: NEWBIE: How do I get the oldest date contained in 3 tables - Mailing list pgsql-general

>> 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