You seem to be coming at SQL with a COBOL perspective. Views are
something
you typically create just once and they stay updated automatically.
They
work like tables not like queries. Assigning variables to each column
of a
view doesn't make any sense (in the SQL sense of "view") as each column
could potentially contain several million values, depending on how many
rows you identify for your VIEW in your definition statement.
You demonstrated your situation with a conditional branch on a value to
produce one of two different . What I think you wanted to do was to
UNION
two queries together so that you could combine the history of a
customer's
account with the current month's activity into a single set of results.
Your queries are also insensitive to year changes. What happens when
you
are in Jan 2006 and you need to review the previous month's data?
Since you are using views I know you are on v5.x or higher. However, I
think you have become so entangled with your subqueries that you have
managed to confuse yourself. Using a subquery to calculate every value
of
each row is VERY inefficient and unless you are actually trying to
prove
just how bad it is, I strongly suggest you modify your approach to
become
more linear, perhaps completely linear.
Here is an example of how to combine two queries into a single result:
(
SELECT fu.customer_id
, fu.month
, sum(fu.usage) total_bandwidth
, sum(if(p.producerID is NULL, 0, fu.usage)) feed_bandwidth
, sum(fu.usage)/sum(if(p.producerID is NULL, 0, fu.usage)) percentage
, count(distinct f.feedID) count
, count(distinct if(p.producerID is null, null, f.feedid) feed_count
FROM feed_usage fu
INNER JOIN customers c
ON fu.customerID=c.customerID
INNER JOIN feeds f
ON fu.feedID=f.feedID
LEFT JOIN producers_join p
ON f.feedID = p.feedID
AND p.producerID IN (3)
GROUP BY fu.month,fu.customerID
)
UNION
(
SELECT customerid
, month
, total_bandwidth
, feed_bandwidth
, percentage
, count
, feed_count
FROM month_totals
)
ORDER BY fu.month DESC;
See how I disentangled so many of your subqueries? If you are having
speed
problems, we can work on that after we get the query working, OK?
ALSO(!)
you don't refer to a value in the outer query by its variable name
(because you normally don't use variables in subqueries), you normally
use
the actual column name in the subquery.
Shawn Green
Database Administrator
Unimin Corporation - Spruce Pine
Dan Rossi <[EMAIL PROTECTED]> wrote on 12/28/2005 01:10:32 AM:
I have an unfinished query, i am trying to test, basically im required
to get the value of the current field in a row and use it for a
subquery in that row :| Its not a working query, and im not asking for
someone to fix it, however as u can see i need to send the customerID
and month to the sub query. What its actually trying to do is tedious
to explain, but i have two tables of media usage for a customer, the
current month will be in the usage table, so that if the plan changes
in that month so does the totals, but for the previous months there is
a static month_totals table showing just the totals recorded. So im
needing to select two different tables depending on what month is
being
selected. I hope this helps.
SELECT SQL_CACHE
CASE WHEN MONTH(mt.month) = MONTH(NOW())
THEN
CREATE VIEW current_month AS
SELECT
@customerID:=c.customerID, @month:=fu.month AS month,
DATE_FORMAT(fu.month,'%M') AS month_long,
@total_bandwidth:=( SELECT SUM(fu.bandwidth) FROM feed_usage fu WHERE
[EMAIL PROTECTED] AND [EMAIL PROTECTED]),
@feed_bandwidth:=( SELECT SUM(fu.bandwidth) FROM feed_usage fu WHERE
[EMAIL PROTECTED] AND [EMAIL PROTECTED] AND fu.feedID IN (SELECT
feedID FROM producers_join WHERE producerID IN (3))),
@percentage:=((@feed_bandwidth/@total_bandwidth)) AS percentage,
@month_totals:=(SELECT month_total FROM month_totals WHERE
[EMAIL PROTECTED] AND DATE_FORMAT(month,"%m")[EMAIL PROTECTED] GROUP BY
month, customerID) AS month_totals,
@count:=(SELECT count(*) FROM feed_usage WHERE [EMAIL PROTECTED]
AND [EMAIL PROTECTED]),
@feed_count:=(SELECT count(*) FROM feed_usage WHERE
[EMAIL PROTECTED] AND [EMAIL PROTECTED] AND feedID IN (SELECT feedID
FROM producers_join WHERE producerID IN (3))),
ROUND(( IF(c.bandwidth_limit=0,
((c.monthly_price/@count)*f.percentage_paid)[EMAIL PROTECTED],
((@[EMAIL PROTECTED])*f.percentage_paid) )),0) AS providers_cut
FROM feed_usage fu INNER JOIN customers c ON
fu.customerID=c.customerID
INNER JOIN feeds f ON fu.feedID=f.feedID WHERE f.feedID IN (SELECT
feedID FROM producers_join WHERE producerID IN (3)) GROUP BY
fu.month,fu.customerID ORDER BY fu.month DESC
ELSE
CREATE VIEW previous_months AS
SELECT
@customerID:=c.customerID, @month:=MONTH(mt.month) AS month,
DATE_FORMAT(mt.month,'%M') AS month_long, @feeds:=feeds,
@total_bandwidth:=( SELECT bandwidth FROM month_totals WHERE
[EMAIL PROTECTED] AND MONTH(month)[EMAIL PROTECTED]),
@feed_bandwidth:=( SELECT bandwidth FROM month_totals INNER JOIN
WHERE
[EMAIL PROTECTED] AND [EMAIL PROTECTED] AND fu.feedID IN (SELECT
feedID FROM producers_join WHERE producerID IN (3))),
@percentage:=((@feed_bandwidth/@total_bandwidth)) AS percentage,
@month_totals:=(SELECT month_total FROM month_totals WHERE
[EMAIL PROTECTED] AND DATE_FORMAT(month,"%m")[EMAIL PROTECTED] GROUP BY
month, customerID) AS month_totals,
@count:=(SELECT count(*) FROM feeds WHERE feedID IN (@feeds)),
@feed_count:=(SELECT count(*) FROM month_totals WHERE
[EMAIL PROTECTED] AND [EMAIL PROTECTED] AND feedID IN (SELECT feedID
FROM producers_join WHERE producerID IN (3))),
ROUND(( IF(c.bandwidth_limit=0,
((c.monthly_price/@count)*f.percentage_paid)[EMAIL PROTECTED],
((@[EMAIL PROTECTED])*f.percentage_paid) )),0) AS providers_cut
FROM feed_usage fu INNER JOIN customers c ON
fu.customerID=c.customerID
INNER JOIN feeds f ON fu.feedID=f.feedID WHERE f.feedID IN (SELECT
feedID FROM producers_join WHERE producerID IN (3)) GROUP BY
fu.month,fu.customerID ORDER BY fu.month DESC
END
On 28/12/2005, at 4:47 PM, [EMAIL PROTECTED] wrote:
Dan Rossi <[EMAIL PROTECTED]> wrote on 12/27/2005 11:39:57 PM:
Hi there i am trying to use usewr variables in a select statement to
add to a where clause in a sub query. Ie
select @id:=id,@month:=month, (select SUM(totals) from table where
[EMAIL PROTECTED] and [EMAIL PROTECTED]) as totals from table
its happened on other occasions ie with calculations and sums, whats
happened in mysql5 ? It used to work in mysql4 , something i am
doing
is wrong ? Please let me know thanks.
Is there a great reason why you are using a subquery? I could rewrite
this
to avoid the subquery and probably eliminate your particular problem:
SELECT id, month, sum(totals) totals FROM TABLE group by id, month;
Unless(!) you oversimplified your original example. In which case,
you
should post your actual query and I can give you a better response.
Technically, the values of the variables should not be determined
until
AFTER the row is processed which means that you shouldn't be able to
use
them for your subquery (at least that's how I remember the SQL:2003
spec
but it's late and I could very well be wrong in my recollection)
Personally, I am not that big a fan of subqueries anyway. There are a
few
types of queries where they make the SQL to achieve a result rather
compact and elegant. However, I have never seen a subquery actually
outperform a properly constructed linear query. They sometimes match
linear performance but most often perform worse to much worse.
Shawn Green
Database Administrator
Unimin Corporation - Spruce Pine
