left-join

问题 I need to left join two tables with a where condition: time_table id rid start_date end_date 1 2 2017-07-01 00:00:00 2018-11-01 00:00:00 2 5 2017-01-01 00:00:00 2017-06-01 00:00:00 3 2 2018-07-01 00:00:00 2020-11-01 00:00:00 record_table id name date 1 record1 2017-10-01 00:00:00 2 record2 2017-02-01 00:00:00 3 record3 2017-10-01 00:00:00 I need to get all those records which are present under given date range. In the above example, I need those records that lie under range for rid = 2 only.

问题 I am working with pretty large dataframes, with as an extreme a dataframe with about 300.000 rows and 1.500 variables. Because of that, when working on those dataframes, I sometimes get the error: Error: cannot allocate vector of size x.x Gb Mostly this means I have to split up my code into smaller steps, or have to change my approach altogether. At the moment I am doing several selections and left_join 's which look something like this: #Subsetting the main dataframe df2 <- select(df1,

问题 Here's a neat one for you (MySQL, obviously): # Setting things up DROP DATABASE IF EXISTS index_test_gutza; CREATE DATABASE index_test_gutza; USE index_test_gutza; CREATE TABLE customer_order ( id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT, invoice MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, PRIMARY KEY(id) ); INSERT INTO customer_order (id, invoice) VALUES (1, 1), (2, 2), (3, 3), (4, 4), (5, 5); CREATE TABLE customer_invoice ( id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT, invoice_no MEDIUMINT

问题 I have a view that is joining two tables and ordering by the first table. Except that the order isn't correct. It misses an occasional record, and then at the end, most of those records exist in order, and then at that end, the rest of the records exist in order. So it has records such as 1 (most of the records in order) 2 4 5 6 7 8 10 11 13 15 3 (the first set of missing records) 12 9 (the rest of the missing records) 14 My view is below. Do I need to do the order by before I do the join?

问题 I have two data frames. The first one has two columns: x is water depth, y is temperature at each depth. The second one has two columns too, x is also water depth, but at different depth compared to that in the first table. The second column z is salinity. I want to join the two tables by x , by adding z to the first table. I have learned how to join tables using 'key' in tidyr , but that only works if the keys are identical. The x in these two tables are not the same. What I want to do is to

问题 I have two data frames. The first one has two columns: x is water depth, y is temperature at each depth. The second one has two columns too, x is also water depth, but at different depth compared to that in the first table. The second column z is salinity. I want to join the two tables by x , by adding z to the first table. I have learned how to join tables using 'key' in tidyr , but that only works if the keys are identical. The x in these two tables are not the same. What I want to do is to

问题 I had the below query working in mysql 4.1, but does not in 5.0: SELECT * FROM email e, event_email ee LEFT JOIN member m on m.email=e.email WHERE ee.email_id = e.email_id The error: 1054 (Unknown column 'e.email' in 'on clause') 回答1: You can only refer the tables previously joined with the JOIN clause in the ON clause. SELECT * FROM email e JOIN event_email ee ON ee.email_id = e.email_id LEFT JOIN member m ON m.email = e.email This can be illustrated better if I put the parentheses around

问题 I have two tables with similar column names and I need to return records from the left table which are not found in the right table? I have a primary key(column) which will help me to compare both tables. Which join is preferred? 回答1: If you are asking for T-SQL then lets look at fundamentals first. There are three types of joins here each with its own set of logical processing phases as: A cross join is simplest of all. It implements only one logical query processing phase, a Cartesian

问题 It is for a system that calculates how the users scan their fingerprints when they enter/leave the workplace. I don't know how it is called in English. I need to determine if the user is late in the morning, and if the user leaves work early. This tb_scan table contains date and time a user scans a fingerprint. CREATE TABLE `tb_scan` ( `scpercode` varchar(6) DEFAULT NULL, `scyear` varchar(4) DEFAULT NULL, `scmonth` varchar(2) DEFAULT NULL, `scday` varchar(2) DEFAULT NULL, `scscantime`

问题 It is for a system that calculates how the users scan their fingerprints when they enter/leave the workplace. I don't know how it is called in English. I need to determine if the user is late in the morning, and if the user leaves work early. This tb_scan table contains date and time a user scans a fingerprint. CREATE TABLE `tb_scan` ( `scpercode` varchar(6) DEFAULT NULL, `scyear` varchar(4) DEFAULT NULL, `scmonth` varchar(2) DEFAULT NULL, `scday` varchar(2) DEFAULT NULL, `scscantime`