join

问题 This question already has answers here : Multiple join conditions using the $lookup operator (4 answers) Closed 2 years ago . I'd like to "join" 3 Collections in MongoDB by using mongochef. The collections are "Order", "Employee" and "City". I tried to use temp collections, but it is not effective. Now I am using var = a for the first "join". If I 'd like to show "a", there are displayed 20 results only. Do you have an idea or another solution? var a = db.Order.aggregate([ { $lookup: { from:

问题 This question already has answers here : Multiple join conditions using the $lookup operator (4 answers) Closed 2 years ago . I'd like to "join" 3 Collections in MongoDB by using mongochef. The collections are "Order", "Employee" and "City". I tried to use temp collections, but it is not effective. Now I am using var = a for the first "join". If I 'd like to show "a", there are displayed 20 results only. Do you have an idea or another solution? var a = db.Order.aggregate([ { $lookup: { from:

问题 Consider following query: SELECT * FROM table1 LEFT JOIN table2 ON table2.some_primary_key = table1.some_primary_key LEFT JOIN table3 ON table3.some_primary_key = table1.some_primary_key OR -- this is the issue table3.column_with_index = table2.column_with_index while I check EXPLAIN it shows me index is not in use for table3 join (however indexes are shown in "possible_keys"). Type: 'ALL'. As per manual: Join type "ALL": A full table scan is done for each combination of rows from the

问题 I'm trying to find any items in column address (users table) that have a match in Address (address_effect table). I'm testing this on my local system with XAMPP (using MariaDB) user table +------------------+-----------------+------------------+--------------------------+ | ID | firstname | lastname | address | | | | | | +----------------------------------------------------------------------------------+ | 1 | john | doe |james street, idaho, usa | | | | | | +---------------------------------

问题 I'm trying to find any items in column address (users table) that have a match in Address (address_effect table). I'm testing this on my local system with XAMPP (using MariaDB) user table +------------------+-----------------+------------------+--------------------------+ | ID | firstname | lastname | address | | | | | | +----------------------------------------------------------------------------------+ | 1 | john | doe |james street, idaho, usa | | | | | | +---------------------------------

问题 I have two MySQL tables: User (id, name) Sale (id, user, item) Where Sale(user) is a foreign key to User(id) , so this is a one-to-many relationship (one user can make many sales). I'm trying to get this from the database and return it in JSON format for multiple users, so it would look like this: [ { "id": 1, "name": "User 1", "sales": [ { "id": 1, "item": "t-shirt" }, { "id": 2, "item": "jeans" } ] }, { "id": 2, "name": "User 2", "sales": [ { "id": 3, "item": "sweatpants" }, { "id": 4,

问题 I have 2 simple mysql tables. The first 1 called mail and has 2 rows: sender | receiver Marley | Bob Saget | Bob The second one called block and has 1 row: blocker | blocked Bob | Marley I want to select sender(s) from the first table who sent Bob emails but aren't blocked in the block table. So the results should be: sender saget I tried the following query but it's not returning results: SELECT * FROM mail LEFT JOIN block ON (block.blocker = 'Bob') WHERE (block.blocked <> mail.sender) 回答1:

问题 I am working on a complex logic where I need to redistribute a quantity from one dataset to another dataset. This questions is a continuation of this question In the example below I am introducing several new dimensions. After aggregating and distributing all the quantities I am expecting the same total quantity however I have some differences. See the example below package playground import org.apache.log4j.{Level, Logger} import org.apache.spark.sql.SparkSession import org.apache.spark.sql

问题 This question already has answers here : How to join (merge) data frames (inner, outer, left, right) (13 answers) Closed 8 days ago . I have two vectors where some elements are common: v1= c('a', 'b', 'c') v2 = c('b', 'c', 'd') I want to combine the vectors into two data.frame s. In the first I want all elements from both vectors, and non-matching positions in either vector should be replaced by NA : v1 v2 a NA b b c c NA d In the second data frame, I want the elements from from the first

问题 This question already has answers here : How to join (merge) data frames (inner, outer, left, right) (13 answers) Closed 8 days ago . I have two vectors where some elements are common: v1= c('a', 'b', 'c') v2 = c('b', 'c', 'd') I want to combine the vectors into two data.frame s. In the first I want all elements from both vectors, and non-matching positions in either vector should be replaced by NA : v1 v2 a NA b b c c NA d In the second data frame, I want the elements from from the first