group-by

问题 I have a table that looks like this: id,created,action 1,'2011-01-01 04:28:21','signup' 2,'2011-01-05 04:28:21','signup' 3,'2011-02-02 04:28:21','signup' How do I select and group these so the output is: year,month,total 2011,1,2 2011,2,1 回答1: Try this: SELECT DATE_FORMAT(created, '%Y') as 'year', DATE_FORMAT(created, '%m') as 'month', COUNT(id) as 'total' FROM table_name GROUP BY DATE_FORMAT(created, '%Y%m') 回答2: SELECT YEAR(created) as year_val, MONTH(created) as month_val ,COUNT(*) as

问题 I have the following linq query, which works fine. I'm not sure how i order the group'd result. from a in Audits join u in Users on a.UserId equals u.UserId group a by a.UserId into g select new { UserId = g.Key, Score = g.Sum(x => x.Score) } the results are currently ordered by UserId ascending. I'm after Score descending. thanks :) 回答1: Just add the orderby clause ;-) from a in Audits join u in Users on a.UserId equals u.UserId group a by a.UserId into g let score = g.Sum(x => x.Score)

问题 I have an object: IObject { string Account, decimal Amount } How do I group by Account and Sum the Amount, returning a List without Linq. 2.0 Framework ... that is why no Linq. Here is what I have: ListofObjects = List<IObject>; foreach (var object in objects) { var objectToAdd = new Object(object); var oa = ListofObjects.Find(x => x.Account == objectToAdd.Account); if (oa == null) { ListofObjects.Add(objectToAdd); } else { ListofObjects.Remove(oa); oa.Amount = objectToAdd.Amount;

问题 I have the below XML <Automobiles> <Cars> <YearofMfr>2010</YearofMfr> <Mileage>12</Mileage> <MeterReading>1500</MeterReading> <Color>Red</Color> <Condition>Excellent</Condition> </Cars> <Cars> <YearofMfr>2010</YearofMfr> <Mileage>12</Mileage> <MeterReading>1500</MeterReading> <Color>Red</Color> <Condition>Excellent</Condition> </Cars> <Cars> <YearofMfr>2008</YearofMfr> <Mileage>11</Mileage> <MeterReading>20000</MeterReading> <Color>Pearl White</Color> <Condition>Good</Condition> </Cars> <

问题 I have two tables, products and meta . They are in relation 1:N where each product row has at least one meta row via foreign key. (viz. SQLfiddle: http://sqlfiddle.com/#!15/c8f34/1) I need to join these two tables but i need to filter only unique products. When I try this query, everything is ok (4 rows returned): SELECT DISTINCT(product_id) FROM meta JOIN products ON products.id = meta.product_id but when I try to select all columns the DISTINCT rule no longer applies to results, as 8 rows

问题 I have two tables, products and meta . They are in relation 1:N where each product row has at least one meta row via foreign key. (viz. SQLfiddle: http://sqlfiddle.com/#!15/c8f34/1) I need to join these two tables but i need to filter only unique products. When I try this query, everything is ok (4 rows returned): SELECT DISTINCT(product_id) FROM meta JOIN products ON products.id = meta.product_id but when I try to select all columns the DISTINCT rule no longer applies to results, as 8 rows

问题 first an example of my table: id_object;time;value;status 1;2014-05-22 09:30:00;1234;1 1;2014-05-22 09:31:00;2341;2 1;2014-05-22 09:32:00;1234;1 ... 1;2014-06-01 00:00:00;4321;1 ... Now i need count all rows with status=1 and id_object=1 monthwise for example. this is my query: SELECT COUNT(*) FROM my_table WHERE id_object=1 AND status=1 AND extract(YEAR FROM time)=2014 GROUP BY extract(MONTH FROM time) The result for this example is: 2 1 2 for may and 1 for june but i need a output with all

问题 I've got the table: SELECT * FROM shop; +---------+--------+------ | article | dealer | price +---------+--------+------ | 0001 | A | 3.45 | 0001 | B | 3.99 | 0002 | A | 10.99 | 0003 | B | 1.45 | 0003 | C | 1.69 | 0003 | D | 1.25 | 0004 | D | 19.95 +---------+--------+------ 7 rows in set (0.20 sec) And I want to get - for each article - the dealer or dealers with the most expensive price. Could anyone tell me why this doesn’t work? SELECT article, dealer, MAX(price) FROM shop GROUP BY

问题 My data has ages, and also payments per month. I'm trying to aggregate summing the payments, but without summing the ages (averaging would work). Is it possible to use different functions for different columns? 回答1: You can pass a dictionary to agg with column names as keys and the functions you want as values. import pandas as pd import numpy as np # Create some randomised data N = 20 date_range = pd.date_range('01/01/2015', periods=N, freq='W') df = pd.DataFrame({'ages':np.arange(N),

问题 The problem I first had with the following query was that the group by clause was performed before the order by : The saved.recipe_id column is an integer generated by UNIX_TIMESTAMP() SELECT saved.recipe_id, saved.`date`, user.user_id FROM saved JOIN user ON user.id = saved.user_id GROUP BY saved.recipe_id ORDER BY saved.`date` DESC So I tried all sorts of different possible solution with sub queries and other bs. In the end I ended up with trying out some different sub queries in the join