>If you can't force PostgreSQL to perform better on the ordered query,
>what about retrieving only the primary keys for the rows you want
>unordered in a subquery and using an "where primaryKey in (...) order
>by ..." statement with ordering the five rows?
>what about retrieving only the primary keys for the rows you want
>unordered in a subquery and using an "where primaryKey in (...) order
>by ..." statement with ordering the five rows?
I appreciate your suggestion but I think I´m misunderstanding something, the select statement should return at about 150.000 rows, why 5 rows?
Guido Neitzer <guido.neitzer@xxxxxxxxxxxxx> escreveu:
On 23.12.2005, at 13:34 Uhr, Carlos Benkendorf wrote:
> For some implementation reason in 8.0.3 the query is returning the
> rows in the correct order even without the order by but in 8.1.1
> probably the implementation changed and the rows are not returning
> in the correct order.
You will never be sure to get rows in a specific order without an
"order by".
I don't know why PG is faster without ordering, perhaps others can
help with that so you don't need a workaround like this:
If you can't force PostgreSQL to perform better on the ordered query,
what about retrieving only the primary keys for the rows you want
unordered in a subquery and using an "where primaryKey in (...) order
by ..." statement with ordering the five rows?
Like this:
select * from mytable where pk in (select pk from mytable where ...)
order by ...;
I don't know whether the query optimizer will flatten this query, but
you can try it.
cug
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