On Sun, Jun 29, 2014 at 10:05:50PM +0800, gotoschool6g wrote:
> The simplified scene:
> select slowfunction(s) from a order by b limit 1;
> is slow than
> select slowfunction(s) from (select s from a order by b limit 1) as z;
> if there are many records in table 'a'.
>
>
> The real scene. Function ST_Distance_Sphere is slow, the query:
> SELECT ST_Distance_Sphere(s, ST_GeomFromText('POINT(1 1)')) from road order
> by c limit 1;
> is slow than:
> select ST_Distance_Sphere(s, ST_GeomFromText('POINT(1 1)')) from (SELECT s
> from road order by c limit 1) as a;
> There are about 7000 records in 'road'. I think to help here I think we need the EXPLAIN ANALYSE output for both queries. Have a nice day, -- Martijn van Oosterhout <klep...@svana.org> http://svana.org/kleptog/ > He who writes carelessly confesses thereby at the very outset that he does > not attach much importance to his own thoughts. -- Arthur Schopenhauer
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