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Joining Three or More Tables

Although each join specification joins only two tables, FROM clauses can contain multiple join specifications. This allows many tables to be joined for a single query.

The ProductVendor table of the AdventureWorks2008R2 database offers a good example of a situation in which joining more than two tables is helpful. The following Transact-SQL query finds the names of all products of a particular subcategory and the names of their vendors:

SELECT p.Name, v.Name
FROM Production.Product p
JOIN Purchasing.ProductVendor pv
ON p.ProductID = pv.ProductID
JOIN Purchasing.Vendor v
ON pv.BusinessEntityID = v.BusinessEntityID
WHERE ProductSubcategoryID = 15
ORDER BY v.Name;

Here is the result set.

Name                           Name

--------------------------------------------------------

LL Mountain Seat/Saddle        Chicago City Saddles

ML Mountain Seat/Saddle        Chicago City Saddles

HL Mountain Seat/Saddle        Chicago City Saddles

LL Road Seat/Saddle         Chicago City Saddles

ML Road Seat/Saddle         Chicago City Saddles

HL Road Seat/Saddle          Chicago City Saddles

LL Touring Seat/Saddle         Chicago City Saddles

ML Touring Seat/Saddle         Chicago City Saddles

HL Touring Seat/Saddle         Chicago City Saddles

HL Touring Seat/Saddle         Expert Bike Co

ML Touring Seat/Saddle         Expert Bike Co

LL Touring Seat/Saddle         Expert Bike Co

HL Road Seat/Saddle            First Rate Bicycles

LL Mountain Seat/Saddle        First Rate Bicycles

ML Mountain Seat/Saddle        First Rate Bicycles

LL Road Seat/Saddle            Hill's Bicycle Service

ML Road Seat/Saddle            Hill's Bicycle Service

HL Mountain Seat/Saddle        Hybrid Bicycle Center

(18 row(s) affected)

Notice that one of the tables in the FROM clause, ProductVendor, does not contribute any columns to the results. Also, none of the joined columns, ProductID and VendorID, appear in the results. Nonetheless, this join is possible only by using ProductVendor as an intermediate table.

The middle table of the join, the ProductVendor table, can be called the translation table or intermediate table, because ProductVendor is an intermediate point of connection between the other tables involved in the join.

When there is more than one join operator in the same statement, either to join more than two tables or to join more than two pairs of columns, the join expressions can be connected with AND or with OR.

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