aggregate-functions | 易学教程

SQL - Select 'n' greatest elements in group

阅读更多关于 SQL - Select 'n' greatest elements in group

The SQL MAX aggregate function will allow you to select the top element in a group. Is there a way to select the top n elements for each group? For instance, if I had a table of users that held their division rank, and wanted the top two users per division ... Users userId | division | rank 1 | 1 | 1 2 | 1 | 2 3 | 1 | 3 4 | 2 | 3 I would want the query to somehow return users 2,3,4 If it matters, I'm using MySQL. select * from users as t1 where (select count(*) from users as t2 where t1.division = t2.division and t2.rank > t1.rank) <2 order by division,rank SELECT * FROM ( SELECT u1.userid, u1

aggregate of an empty result set

阅读更多关于 aggregate of an empty result set

问题 I would like the aggregates of an empty result set to be 0. I have tried the following: SELECT SUM(COALESCE(capacity, 0)) FROM objects WHERE null IS NOT NULL; Result: sum ----- (1 row) Subquestion: wouldn't the above work in Oracle, using SUM(NVL(capacity, 0)) ? 回答1: From the documentation page about aggregate functions: It should be noted that except for count , these functions return a null value when no rows are selected . In particular, sum of no rows returns null, not zero as one might

ios most efficient way to get average value while also filtering out some objects

阅读更多关于 ios most efficient way to get average value while also filtering out some objects

I'm trying to get the average value of an attribute in a child entity while also trying to only include a select set of records. I have two entities in my Core Data model: Invoice and InvoiceDetail. Invoice: invoiceNum - attribute invoiceDate - attribute invoiceDetails - one-to-many relationship to InvoiceDetail InvoiceDetail: itemAmount - attribute itemType - attribute invoice - one-to-one relationship to Invoice If I wanted to just get the average value of itemAmount for an entire invoice, I would use the following (invoice is an NSManagedObject): float avgAmount

Running totals in a SQL view

阅读更多关于 Running totals in a SQL view

I am trying to get running totals in my View in SQL Server 2008 Here is my tables BankAccounts ------------ AccountID (KEY) Name Created Transactions ------------ TransactionID (KEY) Description Credit Debit TransDate Created AccountID Here is my query so far.. SELECT t.Created, t.Description, t.Credit, t.Debit, t.TransDate, t.TransactionID, ba.AccountID, (isnull(t.Credit,0)-isnull(t.Debit,0))+COALESCE((SELECT SUM(isnull(Credit,0)) - SUM(isnull(Debit,0)) FROM Transactions b WHERE b.TransDate < t.TransDate and b.AccountID = t.AccountID),0) AS RunningTotal FROM Transactions t INNER JOIN dbo

Group related records, but pick certain fields from only the first record

阅读更多关于 Group related records, but pick certain fields from only the first record

I'm preforming an aggregate function on multiple records, which are grouped by a common ID. The problem is, I also want to export some other fields, which might be different within the grouped records, but I want to get those certain fields from one of the records (the first one, according to the query's ORDER BY). Starting point example: SELECT customer_id, sum(order_total), referral_code FROM order GROUP BY customer_id ORDER BY date_created I need to query the referral code, but doing it outside of an aggregate function means I have to group by that field as well, and that's not what I want

SQLITE: merging rows into single row if they share a column

阅读更多关于 SQLITE: merging rows into single row if they share a column

问题 From a previous post, I have the following view in sqlite3: CREATE View AttendeeTableView AS SELECT (LastName || " " || FirstName) as AttendeeName, CompanyName, PhotoURI, CompanyAttendeeRelation.CompanyId, CompanyAttendeeRelation.AttendeeId FROM Attendee JOIN CompanyAttendeeRelation on CompanyAttendeeRelation.AttendeeId = Attendee.AttendeeId ORDER BY LastName; Now, since the data is generated from a many-to-many relation between Attendee and Company , I can get results such as: Doe John |

How do I calculate a running SUM on a SQLite query?

阅读更多关于 How do I calculate a running SUM on a SQLite query?

问题 How do I get a column that is the sum of all the values before of another column? 回答1: You can do it by joining the table with itself (performing a so-called Cartesian or cross join). See the following example. SELECT a.name, a.gdppc, SUM(b.gdppc) FROM gdppc AS a, gdppc AS b WHERE b.gdppc <= a.gdppc GROUP BY b.id ORDER BY a.gdppc; Given a table containing countries and their per capita GDP it will give you a running total of the GDP figure. Democratic Republic of Congo|329.645|329.645

Group by column “grp” and compress DataFrame - (take last not null value for each column ordering by column “ord”)

阅读更多关于 Group by column “grp” and compress DataFrame - (take last not null value for each column ordering by column “ord”)

Assuming I have the following DataFrame: +---+--------+---+----+----+ |grp|null_col|ord|col1|col2| +---+--------+---+----+----+ | 1| null| 3|null| 11| | 2| null| 2| xxx| 22| | 1| null| 1| yyy|null| | 2| null| 7|null| 33| | 1| null| 12|null|null| | 2| null| 19|null| 77| | 1| null| 10| s13|null| | 2| null| 11| a23|null| +---+--------+---+----+----+ here is the same sample DF with comments, sorted by grp and ord : scala> df.orderBy("grp", "ord").show +---+--------+---+----+----+ |grp|null_col|ord|col1|col2| +---+--------+---+----+----+ | 1| null| 1| yyy|null| | 1| null| 3|null| 11| # grp:1 - last

SQL Server 2005 Computed Column Result From Aggregate Of Another Table Field's Value

阅读更多关于 SQL Server 2005 Computed Column Result From Aggregate Of Another Table Field's Value

Sorry for the long question title. I guess I'm on to a loser on this one but on the off chance. Is it possible to make the calculation of a calculated field in a table the result of an aggregate function applied to a field in another table. i.e. You have a table called 'mug', this has a child called 'color' (which makes my UK head hurt but the vendor is from the US, what you going to do?) and this, in turn, has a child called 'size'. Each table has a field called sold. The size.sold increments by 1 for every mug of a particular colour and size sold. You want color.sold to be an aggregate of

Django Aggregation - Expression contains mixed types. You must set output_field

阅读更多关于 Django Aggregation - Expression contains mixed types. You must set output_field

问题 I'm trying to achive an Aggregation Query and that's my code: TicketGroup.objects.filter(event=event).aggregate( total_group=Sum(F('total_sold')*F('final_price'))) I have 'total_sold' and 'final_price' in TicketGroup object and all what I want to do is sum and multiply values to get the total sold of all TicketGroups together. All I get is this error: Expression contains mixed types. You must set output_field What I am doing wrong, since I'm calling 'total_group' as my output field? Thanks!