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问题 Here is Sample Data and Schemas CREATE TABLE [dbo].[Customer]( [Id] [int] IDENTITY(1,1) NOT NULL, [Name] [nvarchar](500) NOT NULL, [IsDelete] [bit] NOT NULL, CONSTRAINT [PK_Customer] PRIMARY KEY CLUSTERED ( [Id] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO CREATE TABLE [dbo].[Invoice]([Id] [int] IDENTITY(1,1) NOT NULL,[CustomerId] [int] NOT NULL, [Amount] [decimal](18, 2) NOT NULL,

问题 This is my data frame. acc_index veh_count veh_type 001 1 1 002 2 1 002 2 2 003 2 1 003 2 2 004 1 1 005 2 1 005 2 3 006 1 2 007 2 1 007 2 2 008 2 1 008 2 1 009 3 1 009 3 1 009 3 2 acc_index is unique for each accident veh_count shows how many vehicles are involved in one accident veh_type shows the type of vehicles involved in an accident (1=bicycle, 2=car, 3=bus). What I want to do is to count the number of accidents between cars and bicycles (so, where veh_type=1 and veh_type=9 for the same

问题 This query had reasonable times when the table was small. I'm trying to identify what's the bottleneck, but I'm not sure how to analyze the EXPLAIN results. SELECT COUNT(*) FROM performance_analyses INNER JOIN total_sales ON total_sales.id = performance_analyses.total_sales_id WHERE (size > 0) AND total_sales.customer_id IN ( SELECT customers.id FROM customers WHERE customers.active = 't' AND customers.visible = 't' AND customers.organization_id = 3 ) AND total_sales.product_category_id IN (

问题 forgive me if this is a basic question but i am new to pandas. I have a dataframe with with a column A and i would like to get the top n rows based on the count in Column A. For instance the raw data looks like A B C x 12 ere x 34 bfhg z 6 bgn z 8 rty y 567 hmmu,,u x 545 fghfgj x 44 zxcbv Note that this is just a small sample of the data that i am actually working with. So if we look at Column A, value x appears 4 times,y appears 2 times and z appears 1 time. How can i get the top n values

问题 I found a bunch of similar questions but nothing worked for me, or I am too stupid to get how to do it right. The visit count works fine if I use COUNT(DISTINCT visits.id) but then the vote count goes totally wrong - it displays a value 3 to 4 times larger than it should be. So this is the query SELECT SUM(votes.rating), COUNT(visits.id) FROM topics LEFT JOIN visits ON ( visits.content_id = topics.id ) LEFT JOIN votes ON ( votes.content_id = topics.id ) WHERE topics.id='1' GROUP BY topics.id

问题 So I've started working on a problem where I need to know how many files are in a subfolder of a certain name, that is repeated multiple times in throughout the directory. All folders I want to count have the same name. For example: Main Folder Subfolder Folder I want to count Folder A Folder B Subfolder Folder I want to count Folder C Folder D I'm able to count the number of files in all subfolders recursively, but I don't know how to only look at folders named " Folder I want to count ".

问题 I have a vector A containing years: eg. A <- c(1978, 1979, 1980, 1981, 1984, 1987,1988,1989,1990,1991, 1992) I would like to be able to count the sequence of years before a year is missed out. So I would be looking for my answer to be : 4, 1, 6 I know about using rle for sequences of repeated numbers but not sure what to do here. 回答1: Assuming A is sorted: A <- c(1978, 1979, 1980, 1981, 1984, 1987,1988,1989,1990,1991, 1992) B <- cumsum(c(1, diff(A)>1)) rle(B)$lengths #[1] 4 1 6 来源： https:/

问题 I have a database containing the following tables: - product (product_id / name / price / image_id / description) - order ( order_id / date / status / email ) - order_count ( order_id / product_id / number ) - image (image_id / image_link ) I'd like to show the 3 most sold products on my homepage, but can't wrap my head around doing this. I tried this: $sql = "SELECT" * FROM 'product' INNER JOIN 'afbeelding' WHERE 'product'.'image_id' = 'afbeelding'.'image_id' GROUP BY 'product_id' ORDER BY

问题 Here are examples of the 3 tables I'm working with. Teams +----+------+ | id | name | +----+------+ | 1 | abc | | 2 | def | | 3 | ghi | +----+------+ Members +----+-----------+----------+---------+ | id | firstname | lastname | team_id | +----+-----------+----------+---------+ | 1 | joe | smith | 1 | | 2 | jared | robinson | 1 | | 3 | sarah | cole | 3 | | 4 | jaci | meyers | 2 | +----+-----------+----------+---------+ Goals +----+-----------+ | id | member_id | +----+-----------+ | 1 | 3 | |

问题 I have read much in textbooks and browsed a lot of pages on the internet but I can't understand how functions/operators like min, max, count, ... that aggregate over a relation/table or groups of tuples/rows in a relation/table are built with basic operations such as ∪ (union), ∩ (intersection), x (join), - (minus), π (projection), .... Can anyone show me how to express these functions/operators with relational algebra? 回答1: Computing functions in relation algebra are not fully included yet.