On Aug 24, 2005, at 11:03 PM, Sean Davis wrote:
On 8/24/05 9:46 AM, "Josep Sanmartí" <[EMAIL PROTECTED]>
wrote:
Hello,
I have a 'big' problem:
I have the following table users(name, start_time, end_time), a
new row
is set whenever a user logs into a server. I want to know how many
users have logged in EVERYDAY between 2 different dates. The only
idea
that I have is making several select (one for each day):
SELECT COUNT(name) FROM users WHERE start_time between "startDate"
and "startDate+1"
SELECT COUNT(name) FROM users WHERE start_time between "startDate
+1"
and "startDate+2"
...
I would like to know if its possible to make it in 1 sql statement or
just which is the best efficient way to solve it.
By the way, I use Postgres 7.4.
See:
http://www.postgresql.org/docs/8.0/interactive/sql-select.html#SQL-
UNION
like:
SELECT COUNT(name) FROM users WHERE start_time between "startDate"
and "startDate+1"
union
SELECT COUNT(name) FROM users WHERE start_time between "startDate+1"
and "startDate+2"
I'm guessing he wants something more like this, so he knows which
period is which:
SELECT count_1, count_2
FROM (
SELECT COUNT(name) AS count_1
FROM users
WHERE start_time BETWEEN startDate AND startDate + 1
) as period_1
CROSS JOIN (
SELECT COUNT(name) AS count_2
FROM users
WHERE start_time BETWEEN startDate + 1 AND startDate + 2
) as period_2
Though, you could do the same thing using UNION like this:
SELECT 'period_1'::text as period, COUNT(name) AS num_of_users
FROM users
WHERE start_time BETWEEN startDate AND startDate + 1
UNION
SELECT 'period_2'::text as period, COUNT(name) AS num_of_users
FROM users
WHERE start_time BETWEEN startDate + 1 AND startDate + 2
And of course, using EXPLAIN ANALYZE will help decide which is more
performant.
Michael Glaesemann
grzm myrealbox com
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