Обсуждение: INDEX PROBLEMS ?

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INDEX PROBLEMS ?

От
PostgreSQL Server
Дата:
On postgres 7.2.3 I have found what follows:

explain select * from documents where iddoc>1;

Seq Scan on lotti  (cost=0.00..831.79 rows=26783 width=98)

EXPLAIN
explain select * from documents where iddoc=1;

Index Scan using lotti_pkey on lotti  (cost=0.00..2.26 rows=1 width=98)


Why index is not used for operators > and < ????

Alex

Re: INDEX PROBLEMS ?

От
"Josh Berkus"
Дата:
Alex,

> On postgres 7.2.3 I have found what follows:
> 
> explain select * from documents where iddoc>1;
> 
> Seq Scan on lotti  (cost=0.00..831.79 rows=26783 width=98)
> 
> EXPLAIN
> explain select * from documents where iddoc=1;
> 
> Index Scan using lotti_pkey on lotti  (cost=0.00..2.26 rows=1
> width=98)
> 
> Why index is not used for operators > and < ????

Because ">" is returning 26,000 rows.   When you return that many rows,
a Seq Scan is faster.

-Josh