outer-join

问题 If you consider the (implicit) indexes of each element of a list as their keys, then zipWith is sort of like a relational inner join. It only processes the keys for which both inputs have values: zipWith (+) [1..5] [10..20] == zipWith (+) [1..11] [10..14] == [11,13,15,17,19] Is there a canonical corresponding function corresponding to outer join? Something like: outerZipWith :: (a -> b -> c) -> a -> b -> [a] -> [b] -> [c] outerZipWith _ _ _ [] [] = [] outerZipWith f a' b' [] (b:bs) = f a' b :

问题 Given: (def seq1 ({:id 1 :val 10} {:id 2 :val 20})) (def seq2 ({:id 1 :val 12} {:id 3 :val 30})) Within each sequence, the :id value is guaranteed to be unique in that sequence, though not necessarily ordered. How can these two sequences of maps be joined by the :id key, so that the result is as shown? {1 [{:id 1 :val 10} {:id 1 :val 12}], 2 [{:id 2 :val 20} nil ], 3 [nil {:id 3 :val 30}]} The ultimate result is a map of pairs. This is similar to a full outer join, where not only the

问题 In this example we have 3 related tables on a SQLite database: CREATE TABLE test1 ( c1 integer, primary key (c1) ); CREATE TABLE test2 ( c1 integer, c2 integer, primary key (c1, c2) ); CREATE TABLE test3 ( c2 integer, c3 integer, primary key (c2) ); Now I need to join all tables: test1 -> test2 (with c1 column) test2 -> test3 (with c2 column). I have tried this solution but it doesn't run: SELECT * FROM test1 a LEFT OUTER JOIN test2 b LEFT OUTER JOIN test3 c ON c.c2 = b.c2 ON b.c1=a.c1 It

问题 I am using Oracle SQL, so outer joins have the nice (+) syntax. I should warn you that I am not allowed to redesign the database; I work for a large organization. Here are some example tables: People PersonID Name 1 Elmo 2 Oscar 3 Chris Attribute PersonID Attribute 1 Happy 1 Muppet 1 Popular 2 Grouchy 2 Muppet 2 Popular 3 Programmer I want a list of people and I want to know whether we have knowledge of them being happy or grouchy. The following is the output I want: Name Mood Elmo Happy

问题 Is there any difference between left join and inner join regarding performance? I use SQL Server 2012. 回答1: There is at least one case where LEFT [OUTER] JOIN is a better option than [INNER] JOIN . I talk about getting the same results using OUTER instead of INNER . Example (I am using AdventureWorks 2008 database): -- Some metadata infos SELECT fk.is_not_trusted, fk.name FROM sys.foreign_keys fk WHERE fk.parent_object_id=object_id('Sales.SalesOrderDetail'); GO CREATE VIEW View1 AS SELECT h

问题 I have a Kafka topic where I expect messages with two different key types: old and new. i.e. "1-new" , "1-old" , "2-new" , "2-old" . Keys are unique, but some might be missing. Now using Kotlin and KafkaStreams API I can log those messages with have same key id from new and old. val windows = JoinWindows.of(Duration.of(2, MINUTES).toMillis()) val newStream = stream.filter({ key, _ -> isNew(key) }) .map({key, value -> KeyValue(key.replace(NEW_PREFIX, ""), value) }) val oldStream = stream

问题 It's easy to understand why left outer joins are not commutative, but I'm having some trouble understanding whether they are associative. Several online sources suggest that they are not, but I haven't managed to convince myself that this is the case. Suppose we have three tables: A, B, and C. Let A contain two columns, ID and B_ID, where ID is the primary key of table A and B_ID is a foreign key corresponding to the primary key of table B. Let B contain two columns, ID and C_ID, where ID is

问题 I'm migrating a legacy SQLS2k to 2008R2, and it seems all data access was done through stored procs, and any custom queries use the legacy *= =* outer join syntax. There are upwards of a hundred procs so I don't want to open each one individually to see if it uses that syntax (most wouldn't), is there a way I can query the metadata for a list of procs/functions/views/triggers, then loop through searching for the *= or =* strings, printing out the name of the offending object? My background is

问题 This question already has answers here : LEFT JOIN vs. LEFT OUTER JOIN in SQL Server (12 answers) Closed 4 years ago . What is the difference between Left Join and Left Outer Join ? 回答1: They are the same thing in MySQL. A LEFT JOIN is a synonym or shorthand for LEFT OUTER JOIN . 回答2: There is none. The keyword OUTER is optional. They mean the same. 来源： https://stackoverflow.com/questions/2809594/how-can-we-differ-left-outer-join-vs-left-join

问题 This is coming from converting MSSQL to MySql. The following is code I'm trying to get to work: CREATE TEMPORARY TABLE PageIndex ( IndexId int AUTO_INCREMENT NOT NULL PRIMARY KEY, ItemId VARCHAR(64) ); INSERT INTO PageIndex (ItemId) SELECT Paths.PathId FROM Paths, ((SELECT Paths.PathId FROM AllUsers, Paths WHERE Paths.ApplicationId = @ApplicationId AND AllUsers.PathId = Paths.PathId AND (@Path IS NULL OR Paths.LoweredPath LIKE LOWER(@Path))) AS SharedDataPerPath UNION -- This used to be a