inner-join

问题 I have four tables: foods: id, name users: id, name mealtypes: id, name food_user: id, food_id, user_id, mealtype_id foods and user have a many-to-many relationship mealtype has a one-to-one relationship with food_user In the end I would like to have an instance of a model with the following properties: food.name, users.name, mealtype.name normal sql would be: SELECT f.name, u.name, m.name FROM foods f INNER JOIN food_user fu ON f.id = fu.food_id INNER JOIN users u ON fu.id = u.id INNER JOIN

问题 I have a rather large tibble (called df.tbl with ~ 26k rows and 22 columns) and I want to find the "twins" of each object, i.e. each row that has the same values in column 2:7 (date:Pos). If I use: inner_join(df.tbl, ~ df.tbl[i,], by = c("date", "forge", "serNum", "PinMain", "PinMainNumber", "Pos")) with i being the row I want to check for "twins", everything is working as expected, spitting out a 2 x 22 tibble, and I can expand this using: x <- NULL for (i in 1:nrow(df.tbl)) { x[[i]] <- as

问题 For inner joins , is there any difference in performance to apply a filter in the JOIN ON clause or the WHERE clause? Which is going to be more efficient, or will the optimizer render them equal? JOIN ON SELECT u.name FROM users u JOIN departments d ON u.department_id = d.id AND d.name = 'IT' VS WHERE SELECT u.name FROM users u JOIN departments d ON u.department_id = d.id WHERE d.name = 'IT' Oracle 11gR2 回答1: There should be no difference. The optimizer should generate the same plan in both

问题 For inner joins , is there any difference in performance to apply a filter in the JOIN ON clause or the WHERE clause? Which is going to be more efficient, or will the optimizer render them equal? JOIN ON SELECT u.name FROM users u JOIN departments d ON u.department_id = d.id AND d.name = 'IT' VS WHERE SELECT u.name FROM users u JOIN departments d ON u.department_id = d.id WHERE d.name = 'IT' Oracle 11gR2 回答1: There should be no difference. The optimizer should generate the same plan in both

问题 As brought forwarded from the previous question here. I am using the DTO method to inner join data. Now is it possible to update data at my joined result? How the data will be updated back to the origin table where it should be possible be? Requirement: I am using Entity Framework, C#, ASP.NET Web API I am using SQL Server Currently I successfully joined employee and department table based on their ID . I joined employee and workingshifts based on their shift_id . The inner join query was

问题 There are two dateframes, one is df1, another is df2 as follows: df1: a b id 2010-01-01 1 4 21 2010-01-01 2 5 22 2010-01-01 3 6 23 2010-01-01 4 7 24 2010-01-02 1 4 21 2010-01-02 2 5 22 2010-01-02 3 6 23 2010-01-02 4 7 24 2010-01-03 1 4 21 2010-01-03 2 5 22 2010-01-03 3 6 23 2010-01-03 4 7 24 ........................... df2: c d id 2010-01-02 1 4 21 2010-01-02 2 5 22 2010-01-02 3 6 23 2010-01-02 4 7 24 2010-01-03 1 4 21 2010-01-03 2 5 22 2010-01-03 3 6 23 2010-01-03 4 7 24 ....................

问题 I have a table "channel". channelId a b c d a table "video" videoId | channelId 1 | a 2 | b 3 | c 4 | e a table "comment" commentID | videoID | videoID_channelID xx | 1 | a yy | 2 | b zz | 5 | e tt | 6 | f Keys are: channel.channelId = video.channelId = comment.videoID_channelID video.videoId = comment.videoID I need: all channels with at least 1 video and 1 comment all videos with at least 1 channel and 1 comment all comments with a video and a channel So I want to do 3 SQL statements, one

问题 I have 3 tables called Companies Contacts Campaigns Contacts has foreign key of companies. Companies has foreign key of campaigns. All of them have a column 'name'. I need a join table which will have contact name company name and campaign name. contact id name company_id companies id name campaign_id campaigns id name company_id 回答1: select con.name as contact_name , com.name as company_name,campa.name as campaign_name from contact con inner join company com on con.companyid = com.companyid

问题 The following code will work to select data from two tables: SELECT t1.foo, t2.bar FROM TABLE1 t1 INNER JOIN TABLE2 t2 ON t1.foo=t2.foo I could just as easily written SELECT t2.foo, t2.bar FROM TABLE1 t1 INNER JOIN TABLE2 t2 ON t1.foo=t2.foo t1.foo or t2.foo : six of one or half a dozen of the other. Why not just foo ? I've been wonder why doesn't the SQL server just automatically return the data without me specifying one table or the other since the choice is entirely arbitrary (as far as I

问题 I want to make my insert query which has an inner join to the Users table. The example of the tables is like this: Users: id | fullName | preferredName | email | mobile | password 1 | Pan Lim | Lim | limpan45@gmail.com | 64557812 | passone 2 | Gong My | Gong | gong45@gmail.com | 61345671 | passtwo Orders: id | userid(Foreign key of "id" from Users | timestamp 1 | 1 | 2016-06-10 11:45:31 I'm trying to insert into Orders relating to only knowing the userid from the Users table. It show like