group-by

问题 I have an object that looks something like this: public class Student { public string Name { get; set; } public int Grade { get; set; } } I would like to create the following query: group grades by student name, order each student group by grades, and order groups by max grade in each group. So it will look like this: A 100 A 80 B 80 B 50 B 40 C 70 C 30 I created the following query: StudentsGrades.GroupBy(student => student.Name) .OrderBy(studentGradesGroup => studentGradesGroup.Max(student

问题 I have table in SQL Server. I want to find last row in each group. I tried with the following query, but it does not return exact result. ID column is PK and other columns are set to NOT NULL. select ID, Name FROM (select ID, Name, max(ID) over (partition by Name) as MAX_ID from Customer) x where ID= MAX_ID To be more clear. I have 2 queries.First: ALTER PROCEDURE [dbo].[Ramiz_Musterija_RowNum] @Datum DATE, @BrojKamiona INT AS SET NOCOUNT ON SELECT Ime,MusterijaID,RowNum=ROW_NUMBER() OVER

问题 I have a query that combines a join and a group, but I have a problem. The query is like: var result = from p in Products join bp in BaseProducts on p.BaseProductId equals bp.Id group p by p.SomeId into pg select new ProductPriceMinMax { SomeId = pg.FirstOrDefault().SomeId, CountryCode = pg.FirstOrDefault().CountryCode, MinPrice = pg.Min(m => m.Price), MaxPrice = pg.Max(m => m.Price), BaseProductName = bp.Name <------ can't use bp. }; As you see, it joins the Products table with the

问题 I need to find the latest post for each author and then group the results so I only a single latest post for each author. SELECT wp_posts.* FROM wp_posts WHERE wp_posts.post_status='publish' AND wp_posts.post_type='post' GROUP BY wp_posts.post_author ORDER BY wp_posts.post_date DESC This is correctly grouping the output so I only get one post per author, but it is ordering the results after they have been grouped and not before they have been selected. 回答1: select wp_posts.* from wp_posts

问题 I need to find the latest post for each author and then group the results so I only a single latest post for each author. SELECT wp_posts.* FROM wp_posts WHERE wp_posts.post_status='publish' AND wp_posts.post_type='post' GROUP BY wp_posts.post_author ORDER BY wp_posts.post_date DESC This is correctly grouping the output so I only get one post per author, but it is ordering the results after they have been grouped and not before they have been selected. 回答1: select wp_posts.* from wp_posts

问题 So my dataframe looks like this: from pandas.compat import StringIO d = StringIO(''' date,site,country,score 2018-01-01,google,us,100 2018-01-01,google,ch,50 2018-01-02,google,us,70 2018-01-03,google,us,60 2018-01-02,google,ch,10 2018-01-01,fb,us,50 2018-01-02,fb,us,55 2018-01-03,fb,us,100 2018-01-01,fb,es,100 2018-01-02,fb,gb,100 ''') df = pd.read_csv(d, sep=",") Each site has a different score depending on the country. I'm trying to find the 1/3/5 day difference of scores for each site

问题 I want a "group by and count" command in sqlalchemy. How can I do this? 回答1: The documentation on counting says that for group_by queries it is better to use func.count() : from sqlalchemy import func session.query(Table.column, func.count(Table.column)).group_by(Table.column).all() 回答2: You can also count on multiple groups and their intersection: self.session.query(func.count(Table.column1),Table.column1, Table.column2).group_by(Table.column1, Table.column2).all() The query above will

问题 I have a table (MySQL) that captures samples every n seconds. The table has many columns, but all that matters for this is two: a time stamp (of type TIMESTAMP) and a count (of type INT). What I would like to do, is get sums and averages of the count column over a range of times. For instance, I have samples every 2 seconds recorded, but I would like the sum of the count column for all the samples in a 10 second or 30 second window for all samples. Here's an example of the data: +------------

问题 I want a "group by and count" command in sqlalchemy. How can I do this? 回答1: The documentation on counting says that for group_by queries it is better to use func.count() : from sqlalchemy import func session.query(Table.column, func.count(Table.column)).group_by(Table.column).all() 回答2: You can also count on multiple groups and their intersection: self.session.query(func.count(Table.column1),Table.column1, Table.column2).group_by(Table.column1, Table.column2).all() The query above will

问题 Suppose I have table in Ms Access with following information: ColumnA ColumnB 1 abc 1 pqr 1 xyz 2 efg 2 hij 3 asd My question is, how can I concatenate the values in the second column to a row value based on the first column. The query results that I want is as follows: ColumnA ColumnB 1 abc, pqr, xyz 2 efg, hij 3 asd I want to achieve this through a query. Can someone help me attain this? 回答1: You need a function to do the concatenation. Microsoft Access condense multiple lines in a table