join

问题 I would like to match multiple conditions from independent data tables onto my main data table. How can I do this using the data.table package? What would be the most efficient/fastest way? I have a mock example, with some mock conditions here to illustrate my question: main_data <- data.frame( pnum = c(1,2,3,4,5,6,7,8,9,10), age = c(24,35,43,34,55,24,36,43,34,54), gender = c("f","m","f","f","m","f","m","f","f","m")) data_1 <- data.frame( pnum = c(1,4,5,8,9), value_data_1 = c(1, 2, 1, 1, 1),

问题 I have a skewed data in a table which is then compared with other table that is small. I understood that salting works in case of joins- that is a random number is appended to keys in big table with skew data from a range of random data and the rows in small table with no skew data are duplicated with the same range of random numbers. Hence the the matching happens because there will be a hit in one among the duplicate values for particular slated key of skewed able I also read that salting

问题 I have a skewed data in a table which is then compared with other table that is small. I understood that salting works in case of joins- that is a random number is appended to keys in big table with skew data from a range of random data and the rows in small table with no skew data are duplicated with the same range of random numbers. Hence the the matching happens because there will be a hit in one among the duplicate values for particular slated key of skewed able I also read that salting

问题 I have a view A and a view B . In A I have a lot of information about some systems, like IP and port which I want to preserve all. In B I have just one information that I want to add at A . The matching fields between the two views are IP and Port . So I have to match those hosts which has the same IP and Port in both views. Examples: View A: IP | OS | Hostname | Port | Protocol 1 | Win | hostONE | 80 | tcp 1 | Win | hostONE | 443 | tcp 1 | Win | hostONE | 8080 | tcp 2 | Linux | hostTWO | 21

问题 I have a view A and a view B . In A I have a lot of information about some systems, like IP and port which I want to preserve all. In B I have just one information that I want to add at A . The matching fields between the two views are IP and Port . So I have to match those hosts which has the same IP and Port in both views. Examples: View A: IP | OS | Hostname | Port | Protocol 1 | Win | hostONE | 80 | tcp 1 | Win | hostONE | 443 | tcp 1 | Win | hostONE | 8080 | tcp 2 | Linux | hostTWO | 21

问题 My tables are these : Employee Table: +-----------+----------+------------+ | id | name | department | +-----------+----------+------------+ | 1 | Carrera | 1 | | 2 | Taylor | 1,2 | +-----------+----------+------------+ Department Table: +--------+-------+ | id | name | +--------+-------+ | 1 | CS | | 2 | IT | +--------+-------+ Wanted output from employee table and department table : +----+------------+-------------+ | id | name | department | +----+------------+-------------+ | 1 | Carrera

问题 My tables are these : Employee Table: +-----------+----------+------------+ | id | name | department | +-----------+----------+------------+ | 1 | Carrera | 1 | | 2 | Taylor | 1,2 | +-----------+----------+------------+ Department Table: +--------+-------+ | id | name | +--------+-------+ | 1 | CS | | 2 | IT | +--------+-------+ Wanted output from employee table and department table : +----+------------+-------------+ | id | name | department | +----+------------+-------------+ | 1 | Carrera

问题 I am trying to join two tables: songs id | song | artist ---|------|------- 1 | foo | bar 2 | fuu | bor 3 | fyy | bir score id | score ---|------ 1 | 2 2 | 4 3 | 8 2 | 6 3 | 2 using this SQL command: SELECT songs.id, songs.song, songs.artist, score.score FROM songs LEFT JOIN score ON score.id=songs.id ORDER BY songs.id, score DESC What I get back is duplicates of the same song with multiple scores, I would like the score to be averaged. result id | song | artist | score ---|------|--------|--

问题 I am trying to join two tables: songs id | song | artist ---|------|------- 1 | foo | bar 2 | fuu | bor 3 | fyy | bir score id | score ---|------ 1 | 2 2 | 4 3 | 8 2 | 6 3 | 2 using this SQL command: SELECT songs.id, songs.song, songs.artist, score.score FROM songs LEFT JOIN score ON score.id=songs.id ORDER BY songs.id, score DESC What I get back is duplicates of the same song with multiple scores, I would like the score to be averaged. result id | song | artist | score ---|------|--------|--

问题 I'm working on a project and need to create a few join statements. I tried to make one that selects the maximum value of a column in three different tables. I'm getting an error on the SELECT that says "select is not valid at this server position, expecting FOR, LOCK, TABLE, VALUES, WITH, '('". Not sure what to do, any advice? Code is below. SELECT MAX(cn.TotalDollarPerArea) as 'North Total Dollar per Area', MAX(cs.TotalDollarPerArea) as 'South Total Dollar per Area', MAX(ncl