On May 20, 2009, at 7:17 PM, James B. Byrne wrote:
Looking at this I have to wonder what will be the effect of having
tens of thousands of rate-pairs on file. Would this query be
improved by first doing a sub-query on base/quote pairs that
returned DISTINCT pairs and then do the IN condition
On Thu, May 21, 2009 06:02, Alban Hertroys wrote:
But as people often say here, premature optimisation is a waste of
time, so don't go that route unless you have a reason to expect
problems in that area.
That was my very thought when I sent that message. On the other
hand, in case I was
James B. Byrne wrote:
On Wed, May 20, 2009 13:07, James B. Byrne wrote:
This seems to be working. I had to take a different approach as I
had misapprehended GROUP BY completely.
SELECT *
FROM currency_exchange_rates AS xchg1
WHERE id
IN (
SELECT id
FROM currency_exchange_rates as
James B. Byrne wrote:
On Tue, May 19, 2009 17:43, Andy Colson wrote:
.
What field is the source? currency_code_quote?
-Andy
Here is the layout of the table:
# Table name: currency_exchange_rates
#
# id :integer not null, primary key
# currency_code_base
This seems to be working. I had to take a different approach as I
had misapprehended GROUP BY completely.
SELECT *
FROM currency_exchange_rates AS xchg1
WHERE id
IN (
SELECT id
FROM currency_exchange_rates as xchg2
WHERE
xchg1.currency_code_base = xchg2.currency_code_base
On Wed, May 20, 2009 13:07, James B. Byrne wrote:
This seems to be working. I had to take a different approach as I
had misapprehended GROUP BY completely.
SELECT *
FROM currency_exchange_rates AS xchg1
WHERE id
IN (
SELECT id
FROM currency_exchange_rates as xchg2
WHERE
On Tue, May 19, 2009 17:43, Andy Colson wrote:
.
What field is the source? currency_code_quote?
-Andy
Here is the layout of the table:
# Table name: currency_exchange_rates
#
# id :integer not null, primary key
# currency_code_base :string(3) not
In article 43639.216.185.71.24.1242834374.squir...@webmail.harte-lyne.ca,
James B. Byrne byrn...@harte-lyne.ca writes:
What I want to be able to do is to return the most recent rate for
all unique rate-pairs, irrespective of type. I also have the
requirement to return the 5 most recent rates
I have a requirement to select the effective exchange rate for a
number of currencies as of a specific date and time. The rates may
come from several sources for the same currency. For some
currencies the rate may be set infrequently. I have come close to
getting this to work but cannot seem to
James B. Byrne wrote:
I am perplexed why I cannot select a column from the table without
having to include it in the GROUP BY clause as well.
Any help is welcomed.
Group by is saying I want only one row returned for each distinct value
in this column
so a food table like this:
name |
James B. Byrne wrote:
I have a requirement to select the effective exchange rate for a
number of currencies as of a specific date and time. The rates may
come from several sources for the same currency. For some
currencies the rate may be set infrequently. I have come close to
getting this to
On Tue, May 19, 2009 16:41, Andy Colson wrote:
If your query above is getting you mostly what you want, just use it
as a derived table.
I lack the experience to understand what this means.
If, as you suggest, I use a subquery as the expression to the main
SELECT and for it I use the syntax
On Tue, May 19, 2009 17:02, Andy Colson wrote:
so: select max(name), type from food group by type
works cuz we only get one name (the max name) back for each type.
or: select name, type from food group by type, name
which in our example is kinda pointless, but still, give us the
distinct
James B. Byrne wrote:
On Tue, May 19, 2009 16:41, Andy Colson wrote:
If your query above is getting you mostly what you want, just use it
as a derived table.
I lack the experience to understand what this means.
If, as you suggest, I use a subquery as the expression to the main
SELECT and
James B. Byrne wrote:
On Tue, May 19, 2009 17:02, Andy Colson wrote:
so: select max(name), type from food group by type
works cuz we only get one name (the max name) back for each type.
or: select name, type from food group by type, name
which in our example is kinda pointless, but still,
James B. Byrne wrote:
I have a requirement to select the effective exchange rate for a
number of currencies as of a specific date and time. The rates may
come from several sources for the same currency. For some
currencies the rate may be set infrequently. I have come close to
getting this to
Andy Colson wrote:
James B. Byrne wrote:
I have a requirement to select the effective exchange rate for a
number of currencies as of a specific date and time. The rates may
come from several sources for the same currency. For some
currencies the rate may be set infrequently. I have come
On May 19, 2009, at 11:29 PM, Andy Colson wrote:
I'm not sure what this will do:
HAVING
COUNT(fxr.currency_code_quote) = 1
The only time I have ever used HAVING is like:
select name from something group by name having count(*) 1
to find duplicate name's.
That will leave out all
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