Probably this explains the ERROR for the last query... The ORDER BY
and LIMIT clauses are expected to end a query (except for subqueries,
of course), and hence the keyword UNION is not expected after the
LIMIT clause...
On 6/18/06, Tom Lane <[EMAIL PROTECTED]> wrote:
Joe Conway <[EMAIL PROTECTED]> writes:
> I was trying to work around limitations with "partitioning" of tables
> using constraint exclusion, when I ran across this little oddity:
I think you're under a misimpression about the syntax behavior of ORDER
BY and UNION. Per spec, ORDER BY binds less tightly than UNION, thus
select foo union select bar order by x
means
(select foo union select bar) order by x
If you want to apply ORDER BY to either arm of a union individually,
you need parentheses, eg
(select foo order by x) union (select bar order by x)
(Note that this construct fails to guarantee that the output of the
union will be sorted by x!) LIMIT is not in the spec but we treat
it like ORDER BY for this purpose.
To guarantee the ordering, one can use
select * from (select foo from A union select bar from B) order by x
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