inner-join

问题 First Query: Select * from table1 inner join table2 on table1.Id = table2.Id Second Query: Select * from table1, table2 where table1.Id = table2.Id What is difference between these query regarding performance which should one use? 回答1: The two statements you posted are logically identical. There isn't really a practical reason to prefer one over the other, it's largely a matter of personal style and readability. Some people prefer the INNER JOIN syntax and some prefer just to use WHERE.

问题 So I have four tables. Each table has a single id for the previous table id. So my in click table has an id and an id for the ad from which it came. In the ad table, it has an id for the ad and one for the campaign it's from. So here's an example. Table4 - id company table_id 11 hp 20 12 apple 23 13 kohls 26 14 target 21 15 borders 28 Table3 - id value table2_id 21 ks 53 22 al 54 23 tx 53 24 fl 55 25 co 51 Table2 - id value table1_id 51 ks 34 52 al 34 53 tx 33 54 fl 35 55 co 31 Table1 - id

问题 I'm usually pretty well versed with JOINS, but this is new. Suppose three tables (classic case of two tables and a third, linker table): Customer Product Transaction -------- ------- ----------- ID ID CustomerID Name Desc ProductID Cost Date (Simplistic on purpose, I can't reproduce the actual structure, it's not my code.) Normally, to get a table of "who bought what when", I'd do this: SELECT Customer.Name, Product.Desc, Transaction.Date FROM Product INNER JOIN Transaction ON Transaction

问题 I've got the basics of LINQ-to-SQL down, but I've been struggling trying to get JOINs to work properly. I'd like to know how to convert the following to LINQ-to-SQL (ideally using method chaining, as that is my preferred format). SELECT c.CompanyId, c.CompanyName, p.FirstName + ' ' + p.LastName as AccountCoordinator, p2.FirstName + ' ' + p2.LastName as AccountManager FROM dbo.Companies c INNER JOIN dbo.Persons p ON c.AccountCoordinatorPersonId = p.PersonId INNER JOIN dbo.Persons p2 ON c

问题 I've got the basics of LINQ-to-SQL down, but I've been struggling trying to get JOINs to work properly. I'd like to know how to convert the following to LINQ-to-SQL (ideally using method chaining, as that is my preferred format). SELECT c.CompanyId, c.CompanyName, p.FirstName + ' ' + p.LastName as AccountCoordinator, p2.FirstName + ' ' + p2.LastName as AccountManager FROM dbo.Companies c INNER JOIN dbo.Persons p ON c.AccountCoordinatorPersonId = p.PersonId INNER JOIN dbo.Persons p2 ON c

问题 I have this code User.find(:all, :limit => 10, :joins => :user_points, :select => "users.*, count(user_points.id)", :group => "user_points.user_id") which generates following sql SELECT users.*, count(user_points.id) FROM `users` INNER JOIN `user_points` ON user_points.user_id = users.id GROUP BY user_points.user_id LIMIT 10 is it possible to make LEFT JOIN instead of INNER JOIN other way than User.find_by_sql and manualy typing the query? 回答1: You can try this User.find(:all, limit: 10,

问题 I have this code User.find(:all, :limit => 10, :joins => :user_points, :select => "users.*, count(user_points.id)", :group => "user_points.user_id") which generates following sql SELECT users.*, count(user_points.id) FROM `users` INNER JOIN `user_points` ON user_points.user_id = users.id GROUP BY user_points.user_id LIMIT 10 is it possible to make LEFT JOIN instead of INNER JOIN other way than User.find_by_sql and manualy typing the query? 回答1: You can try this User.find(:all, limit: 10,

问题 Assuming that I have the following T-SQL code: SELECT * FROM Foo f INNER JOIN Bar b ON b.BarId = f.BarId; WHERE b.IsApproved = 1; The following one also returns the same set of rows: SELECT * FROM Foo f INNER JOIN Bar b ON (b.IsApproved = 1) AND (b.BarId = f.BarId); This might not be the best case sample here but is there any performance difference between these two? 回答1: No, the query optimizer is smart enough to choose the same execution plan for both examples. You can use SHOWPLAN to check

问题 I want to delete using INNER JOIN in SQL Server 2008 . But I get this error: Msg 156, Level 15, State 1, Line 15 Incorrect syntax near the keyword 'INNER'. My code: DELETE FROM WorkRecord2 INNER JOIN Employee ON EmployeeRun=EmployeeNo WHERE Company = '1' AND Date = '2013-05-06' 回答1: You need to specify what table you are deleting from, here is a version with an alias: DELETE w FROM WorkRecord2 w INNER JOIN Employee e ON EmployeeRun=EmployeeNo WHERE Company = '1' AND Date = '2013-05-06' 回答2:

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