Use of Indicies ...

Always something that confuses me ... I have a query that looks like:

SELECT count(counter_id) \ FROM referrer_link \WHERE counter_id = ? \  AND referrer_id = ? \  AND stat_date = ?;

There is an index on all three conditions in the WHERE clause:

Yet EXPLAIN shows:

Aggregate  (cost=2.05 rows=1 width=4) ->  Index Scan using referrer_link_counter_id on referrer_link  (cost=2.05 rows=1
width=4)

EXPLAIN

Table looks like:

webcounter=> \d referrer_link
Table    = referrer_link
+----------------------------------+----------------------------------+-------+
|              Field               |              Type                | Length|
+----------------------------------+----------------------------------+-------+
| counter_id                       | int4                             |     4 |
| stat_date                        | datetime                         |     8 |
| referrer_id                      | int4                             |     4 |
| referrer_hits                    | int8                             |     8 |
+----------------------------------+----------------------------------+-------+
Indices:  referrer_link_counter_id         referrer_link_referrer_id         referrer_link_stat_date

Why does EXPLAIN only show the use of one of the indices, why counter_id
and why not all three?


Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org 
primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org