I have a table with a CreatedDate column. I want to order by the rows that have been in the database the longest, but need to determine the number of days by subtracting it from DateTime.Now.
I realise this is doable simply by ordering by the CreatedDate, but I need to do more than that.
I need to order the items by the amount of times they have been used within a period of time, in effect getting the most popular items.
So what I want to do is first determine the number of days, and after that divide this by the number of times each item has been used.
Step 1)
orderby (DateTime.Now.Subtract(t.CreatedDate.Value).Days)
Step 2)
orderby (t.UsedCount/DateTime.Now.Subtract(t.CreatedDate.Value).Days)
This results in the following error:
Method 'System.TimeSpan Subtract(System.DateTime)' has no supported translation to SQL.
Oddly, "Subtract()" doesn't work, but Minus does.
try:
orderby (t.UsedCount/(DateTime.Now - t.CreatedDate.Value).Days)
(Tested in LINQPad using the "master" database)
from sp in Spt_monitors
orderby sp.Io_busy / (DateTime.Now - sp.Lastrun).Days
select sp
Related
I need someone who can explain me about "group function is not allowed here" because I don't understand it and I would like to understand it.
I have to get the product name and the unit price of the products that have a price above the average
I initially tried to use this, but oracle quickly told me that it was wrong.
SELECT productname,unitprice
FROM products
WHERE unitprice>(AVG(unitprice));
search for information and found that I could get it this way:
SELECT productname,unitprice FROM products
WHERE unitprice > (SELECT AVG(unitprice) FROM products);
What I want to know is why do you put two select?
What does group function is not allowed here mean?
More than once I have encountered this error and I would like to be able to understand what to do when it appears
Thank you very much for your time
The phrase "group function not allowed here" is referring to anything that is in some way an "aggregation" of data, eg SUM, MIN, MAX, etc et. These functions must operate on a set of rows, and to operate on a set of rows you need to do a SELECT statement. (I'm leaving out UPDATE/DELETE here)
If this was not the case, you would end up with ambiguities, for example, lets say we allowed this:
select *
from products
where region = 'USA'
and avg(price) > 10
Does this mean you want the average prices across all products, or just the average price for those products in the USA? The syntax is no longer deterministic.
Here's another option:
SELECT *
FROM (
SELECT productname,unitprice,AVG(unitprice) OVER (PARTITION BY 1) avg_price
FROM products)
WHERE unitprice > avg_price
The reason your original SQL doesn't work is because you didn't tell Oracle how to compute the average. What table should it find it in? What rows should it include? What, if any, grouping do you wish to apply? None of that is communicated with "WHERE unitprice>(AVG(unitprice))".
Now, as a human, I can make a pretty educated guess that you intend the averaging to happen over the same set of rows you select from the main query, with the same granularity (no grouping). We can accomplish that either by using a sub-query to make a second pass on the table, as your second SQL did, or the newer windowing capabilities of aggregate functions to internally make a second pass on your query block results, as I did in my answer. Using the OVER clause, you can tell Oracle exactly what rows to include (ROWS BETWEEN ...) and how to group it (PARTITION BY...).
So i built a query for my leadership team that was correct, but i dont understand why oracle gave me the correct answer.
i have 3 tables that i needed to get data out of in order to get the total billed amount.
Here is my query (please forgive me, my 2nd post and im not sure how to properly format my querys)
select b.total_amount_billed as billed from t1.billing_information b
where b.billing_no in
(select h.billing_no
from t1.res_history h where h.res_seq_no in
(Select r.reservation_seq_no
from t1.res r where r.customer_order_no in ('THO40000') ))
so in the deepest select, i take the the sequence number where my customer order number was THO40000, this query returns 2 sequence numbers.
the second sub query returns the billing numbers for my order from the history table where the sequence number match, in this case for this order they both use the same billing number, 312000.
the final select, returns my total billed amount where it matched my billing numbers it found, in my case $110.
the query works, but what i dont understand is why is it not duplicated? why does it not return 110, for each time it found 312000, giving me 2 records of 110? the billing number is a PK in the billing_information table. im not sure why it worked without me using the distinct keyword on the query for the billing number.
anyway thanks for the help, ill do my best to explain if you have questions!
You are being saved because you used IN to get the billing_no values to use, rather than an INNER JOIN between the two tables using b.billing_no = h.billing_no. A join would have duplicated the records, but your IN query is essentially this:
select b.total_amount_billed as billed
from t1.billing_information b
where b.billing_no in (312000, 312000);
If there is a single row in billing_information having billing_no equal to 312000, it is in the list, so the WHERE condition is true and it is included in the results. The fact that it is in the list twice doesn't make the IN condition "more true".
Crosstab report works 99%.
About 20 rows, all but one are ok.
5 columns - Company Division.
The rows are things like cost, revenue, revenue 2, etc.
All the rows that work have three attributes I'm using to select them:
Fiscal Year
Period
Solution.
The problem is there is table that lists an YTD rate for each period. This table is not Division Specific; it's company wide.
All the tables are linked to the accounting period table that has fiscal year and period. So the overall query limits data to fiscal year (?pFiscalYear?) and period <= ?pPeriod?, based on prompt page results.
The source table has this:
FY_CD PD_NO ACT_CURR_RT ACT_YTD_RT
2018 1 0.36121715 0.36121715
2018 2 0.32471476 0.34255512
2018 3 0.25240906 0.31210183
2018 4 0.33154745 0.31925874
Note the YTD rate is not an average of any of the other numbers.
When I select the ACT_YTD_RT, as a row, I want the ACT_YTD_RT that matches the selected period.
What I get is the average if I set the aggregation to average or the lowest if I set it to other aggregations. So sometimes, it looks right (if I run for period 1,2,3, as the rate kept falling), and sometimes it's wrong (period 4
returns .3121 instead of .3192).
I've tried a number of different methods and can generate garbage data (totals, min, max, average) and crossjoins but can't figure out how to get the value I'm looking for.
I want YTD_RT where fiscal year =?pFiscal? and period = ?pPeriod?.
I tried a straight if then clause:
if (sourcetable.fiscalYear = ?pFiscalYear?) and (sourcetable.Period = ?pPeriod?) then (ACT_YTD_RT)
but I get an error like this:
'ACT_YTD_RT' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause. (SQLSTATE=42000, SQLERRORCODE=8120)
If I create another query that generates the right response and try to include it, I get a crossjoin error that the query I'm referencing is trying to crossjoin several other items in the crosstab query.
A union doesn't work (different number of columns).
Not sure how a join would work since the division doesn't exist in the rate table.
I maybe could create a view in the database that did a crossjoin of the division table and the rate table, add that to the framework and then I wouldn't have a crossjoin since the solution would be in the rate "table" (really view), but that seems wrong somehow.
If I could just write a freaking parameterized query direct to the database I'd be done. But in Cognos 11 crosstabs I can't find a place for a SQL query object. And that shouldn't be necessary.
I've spent hours and hours chasing this in circles.
Anybody have any ideas?
Thanks
Paul
So the earlier problem was that this:
if (sourcetable.fiscalYear = ?pFiscalYear?) and (sourcetable.Period = ?pPeriod?) then (ACT_YTD_RT)
Generated an error like this:
'ACT_YTD_RT' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause. (SQLSTATE=42000, SQLERRORCODE=8120)
To fix the above, I had to add a cross join of the division table and the rate table as a view in the database. Then add that to the framework. Then build the data item this way:
total (
if (sourcetable.fiscalYear = ?pFiscalYear?) and (sourcetable.Period = ?pPeriod?) then (ACT_YTD_RT)
)
And now the "total" provides the missing group by. And the crossjoin in the database provides the division information so the crosstab is happy.
I still think there should have been an easier way to do this, but I have a functioning hammer at the moment.
Running this line of code
Activity.uniq.select(:ip).where("created_at > NOW() - INTERVAL 1 DAY").count
Returns the number of all lines (without the uniquness filter) although the SQL is correct (with the DISTINCT keyword)
If I run this command in 2 steps:
c = Activity.uniq.select(:ip).where("created_at > NOW() - INTERVAL 1 DAY")
c.size
Then I get the right count.
How can it be?
Thank you
Generally DISTINCT will remove duplicate results from a result set but it won't do any grouping. Since you have one row in a COUNT result, you won't see any effect. What you really want is this:
SELECT COUNT(DISTINCT activities.ip) FROM activities WHERE ...
Note that you want a count of the distinct activities, not a distinct count.
I'm not sure how you'd manage to emit this SQL using ActiveRecord. You may need to resort to using the ActiveRecord connection directly and use select_value for such an unusual sort of inquiry unless you can coach select to do it for you.
I could use this query to select all orders with a date on a monday:
SELECT * from orders WHERE strftime("%w", date)="1";
But as far as I know, this can't be speed up using an index, as for every row strftime has to be calculated.
I could add an additional field with the weekday stored, but I want to avoid it. Is there a solution that makes use of an index or am I wrong and this query actually works fine? (That means it doesn't have to go through every row to calculate the result.)
If you want all Mondays ever, you'd need a field or sequential scan. What you could do, is calculate actual dates for example for all Mondays within a year. The condition WHERE date IN ('2009-03-02', '2009-02-23', ...) would use index
Or as an alternative to vartec's suggestion, construct a calendar table consisting only of a date and a day name for each day in the year (both indexed) and then perform your query by doing a JOIN against this table.