Understanding what an inner join query produces

[Steve Holdorf]

Below is a multi inner join query that works. The problem is that I don't understand how it is evaluated and need help understanding what it is doing. Can someone explain in detail what the query is doing because I don't quite understand? SELECT DISTINCT o.OrderDate, c.CompanyName, od.Quantity, p.ProductName FROM Customers AS c INNER JOIN Orders AS o ON o.CustomerID = c.CustomerID INNER JOIN [Order Details] AS od ON od.OrderID = o.OrderID INNER JOIN Products AS p ON p.ProductID = od.ProductID Thanks, Steve Holdorf

[Mycroft Holmes]

There used to be a good article on CP explaining join types but I couldn't find it, this returns[^] what should help Basically an inner join returns records that have the same values in the tables on each side of the join. Orderdetail => product There will be a foriegn key constraint on the OD table that says an orderid cannot be entered unless there is a product record, therefore this join will no do any filtering but will be used as a lookup to get the productname for each orderdetail. Order => Orderdetail This gets the detail records for each order record and will be a 1 to many join. Customer => Order is the same as order/detail join

Never underestimate the power of human stupidity RAH

[Lost User]

Mycroft is referring to this[^] article.

I are Troll :)

[Mycroft Holmes]

Thanks Eddy, that is exactly the article I was after, have to bookmark it for future reference.

Never underestimate the power of human stupidity RAH

[Lost User]

You're welcome :)

[Not Active]

A very good reference book for this subject is Inside Microsoft® SQL Server® 2008: T-SQL Querying[^]

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