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(at)hub(dot)org secondary: scrappy(at){freebsd|postgresql}.org