Module 4:Joining Data from

Multiple Tables

Module 4: Joining Data from Multiple Tables

• Querying Multiple Tables by Using Joins

• Applying Joins for Typical Reporting Needs

• Combining and Limiting Result Sets

Lesson 1: Querying Multiple Tables by Using Joins

• Fundamentals of Joins

• Categorizing Statements by Types of Joins

• Joining Data Using Inner Joins

• Joining Data Using Outer Joins

• Joining Data Using Cross Joins

• Identifying the Potential Impact of a Cartesian Product

Fundamentals of Joins

• Select Specific Columns from Multiple Tables• JOIN keyword specifies that tables are joined and how

to join them

• ON keyword specifies join condition

FROM first_table join_type second_table [ON (join_condition)]FROM first_table join_type second_table [ON (join_condition)]

Joins:

Simplified JOIN Syntax:

• Query Two or More Tables to Produce a Result Set• Use Primary and Foreign Keys as join conditions

• Use columns common to specified tables to join tables

Categorizing Statements by Types of Joins

• Inner Join

Includes equi-joins and natural joins

Use comparison operators to match rows

• Outer Join

Includes left, right, or full outer joins

• Cross Join

Also called Cartesian products

• Self Join

Refers to any join used to join a table to itself

Joining Data Using Inner Joins

SELECT e.LoginIDFROM HumanResources.Employee AS e INNER JOIN Sales.SalesPerson AS s ON e.BusinessEntityID = s.BusinessEntityID

SELECT e.LoginIDFROM HumanResources.Employee AS e INNER JOIN Sales.SalesPerson AS s ON e.BusinessEntityID = s.BusinessEntityID

LoginID-------------------------adventure-works\syed0adventure-works\david8adventure-works\garrett1...(17 row(s) affected)

LoginID-------------------------adventure-works\syed0adventure-works\david8adventure-works\garrett1...(17 row(s) affected)

• An inner join is a join in which the values in the columns being joined are compared using a comparison operator

Result Set:

Example:

Joining Data Using Outer Joins

SELECT p.Name, pr.ProductReviewIDFROM Production.Product pLEFT OUTER JOIN Production.ProductReview prON p.ProductID = pr.ProductID

SELECT p.Name, pr.ProductReviewIDFROM Production.Product pLEFT OUTER JOIN Production.ProductReview prON p.ProductID = pr.ProductID

• Outer Joins return all rows from at least one of the tables or views mentioned in the FROM clause

Name ProductReviewID----------------------------------Adjustable Race NULLBearing Ball NULL...(505 row(s) affected)

Name ProductReviewID----------------------------------Adjustable Race NULLBearing Ball NULL...(505 row(s) affected)

Example:

Result Set:

Joining Data Using Cross Joins

SELECT p.BusinessEntityID, t.Name AS TerritoryFROM Sales.SalesPerson pCROSS JOIN Sales.SalesTerritory tORDER BY p.BusinessEntityID

SELECT p.BusinessEntityID, t.Name AS TerritoryFROM Sales.SalesPerson pCROSS JOIN Sales.SalesTerritory tORDER BY p.BusinessEntityID

• In a Cross Join, each row from the left table is combined with all rows from the right table

BusinessEntityID Territory----------------------------274 Northwest274 Northeast...(170 row(s) affected)

BusinessEntityID Territory----------------------------274 Northwest274 Northeast...(170 row(s) affected)

Example:

Result Set:

Use CROSS JOINs with caution if you do not need a true Cartesian ProductUse CROSS JOINs with caution if you do not need a true Cartesian Product

Identifying the Potential Impact of a Cartesian Product

• Is defined as all possible combinations of rows in all tables

A Cartesian Product:

• Results in a rowset containing the number of rows in the first table times the number of rows in the second

• Can result in huge result sets that take several hours to complete!

Demonstration: Querying a Table Using Joins

In this demonstration, you will see how to:

• Query the Table Using an Inner Join

• Query the Table Using an Outer Join

• Query the Table Using a Cross Join

Lesson 2: Applying Joins for Typical Reporting Needs

• Joining Three or More Tables

• Joining a Table to Itself

• Joining Tables by Using Non-Equi Joins

• Joining Tables in a User-Defined Function

Joining Three or More Tables

SELECT p.Name, v.NameFROM Production.Product pJOIN Purchasing.ProductVendor pvON p.ProductID = pv.ProductIDJOIN Purchasing.Vendor vON pv.BusinesEntityID = v.BusinessEntityIDWHERE ProductSubcategoryID = 15ORDER BY v.Name

SELECT p.Name, v.NameFROM Production.Product pJOIN Purchasing.ProductVendor pvON p.ProductID = pv.ProductIDJOIN Purchasing.Vendor vON pv.BusinesEntityID = v.BusinessEntityIDWHERE ProductSubcategoryID = 15ORDER BY v.Name

Example:

• FROM clauses can contain multiple Join specifications which allows many tables to be joined in a single Query

Name Name-----------------------------------------------LL Mountain Seat/Saddle Chicago City SaddlesML Mountain Seat/Saddle Chicago City Saddles...(18 row(s) affected)

Name Name-----------------------------------------------LL Mountain Seat/Saddle Chicago City SaddlesML Mountain Seat/Saddle Chicago City Saddles...(18 row(s) affected)

Result Set:

Joining a Table to Itself

SELECT DISTINCT pv1.ProductID, pv1.BusinessEntityIDFROM Purchasing.ProductVendor pv1INNER JOIN Purchasing.ProductVendor pv2ON pv1.ProductID = pv2.ProductID AND pv1.BusinessEntityID <> pv2.BusinessEntityIDORDER BY pv1.ProductID

SELECT DISTINCT pv1.ProductID, pv1.BusinessEntityIDFROM Purchasing.ProductVendor pv1INNER JOIN Purchasing.ProductVendor pv2ON pv1.ProductID = pv2.ProductID AND pv1.BusinessEntityID <> pv2.BusinessEntityIDORDER BY pv1.ProductID

• A Table can be Joined to itself by using a Self-Join

ProductID BusinessEntityID------------------------------317 1578317 1678...(347 row(s) affected)

ProductID BusinessEntityID------------------------------317 1578317 1678...(347 row(s) affected)

Result Set:

Example:

Joining Tables by Using Non-Equi Joins

SELECT DISTINCT p1.ProductSubcategoryID, p1.ListPriceFROM Production.Product p1 INNER JOIN Production.Product p2 ON p1.ProductSubcateogoryID = p2.ProductSubcategoryID AND p1.ListPrice <> p2.ListPriceWHERE p1.ListPrice < $15 AND p2.ListPrice < $15ORDER BY ProductSubcategoryID

SELECT DISTINCT p1.ProductSubcategoryID, p1.ListPriceFROM Production.Product p1 INNER JOIN Production.Product p2 ON p1.ProductSubcateogoryID = p2.ProductSubcategoryID AND p1.ListPrice <> p2.ListPriceWHERE p1.ListPrice < $15 AND p2.ListPrice < $15ORDER BY ProductSubcategoryID

• The same Operators and Predicates used for Inner Joins can be used for Not-Equal Joins

Example:

ProductSubcateogoryID ListPrice-----------------------------------23 8.9923 9.50...(8 row(s) affected)

ProductSubcateogoryID ListPrice-----------------------------------23 8.9923 9.50...(8 row(s) affected)

Result Set:

SELECT * FROM Sales.ufn_SalesByStore (29825)SELECT * FROM Sales.ufn_SalesByStore (29825)

Joining Tables in a User-Defined Function

CREATE FUNCTION Sales.ufn_SalesByStore (@storeid int)RETURNS TABLE AS RETURN ( SELECT P.ProductID, P.Name, SUM(SD.LineTotal) AS 'YTD Total‘ FROM Production.Product AS P JOIN Sales.SalesOrderDetail AS SD ON SD.ProductID = P.ProductID JOIN Sales.SalesOrderHeader AS SH ON SH.SalesOrderID = SD.SalesOrderID WHERE SH.CustomerID = @storeid GROUP BY P.ProductID, P.Name );

CREATE FUNCTION Sales.ufn_SalesByStore (@storeid int)RETURNS TABLE AS RETURN ( SELECT P.ProductID, P.Name, SUM(SD.LineTotal) AS 'YTD Total‘ FROM Production.Product AS P JOIN Sales.SalesOrderDetail AS SD ON SD.ProductID = P.ProductID JOIN Sales.SalesOrderHeader AS SH ON SH.SalesOrderID = SD.SalesOrderID WHERE SH.CustomerID = @storeid GROUP BY P.ProductID, P.Name );

• User-defined functions can be used to focus, simplify, and customize the perception each user has of the database

Product ID Name YTD Total------------------------------------------------707 Sport-100 Helmet, Red 620.250910708 Sport-100 Helmet, Black 657.636610

Product ID Name YTD Total------------------------------------------------707 Sport-100 Helmet, Red 620.250910708 Sport-100 Helmet, Black 657.636610

Example:

Result Set:

Demonstration: Joining Tables

In this demonstration, you will see how to:

• Join Three or More Tables

• Join a Table to Itself

• Join a Table using a Non-Equi Join

Lesson 3: Combining and Limiting Result Sets

• Combining Result Sets by Using the UNION Operator

• Limiting Result Sets by Using the EXCEPT and INTERSECT Operators

• Identifying the Order of Precedence of UNION, EXCEPT, and INTERSECT

• Limiting Result Sets by Using the TOP and TABLESAMPLE Operators

• Categorizing Statements that Limit Result Sets

Combining Result Sets by Using the UNION Operator

SELECT * FROM testaUNION ALLSELECT * FROM testb;

SELECT * FROM testaUNION ALLSELECT * FROM testb;

The number and order of columns must be the same

in all queries and all data types must be compatible

The number and order of columns must be the same

in all queries and all data types must be compatible

• UNION combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the union

Example:

columna columnb------------------100 test100 test...(8 row(s) affected)

columna columnb------------------100 test100 test...(8 row(s) affected)

Result Set:

Limiting Result Sets by Using the EXCEPT and INTERSECT Operators

SELECT ProductID FROM Production.ProductEXCEPTSELECT ProductID FROM Production.WorkOrder

SELECT ProductID FROM Production.ProductEXCEPTSELECT ProductID FROM Production.WorkOrder

SELECT ProductID FROM Production.ProductINTERSECTSELECT ProductID FROM Production.WorkOrder

SELECT ProductID FROM Production.ProductINTERSECTSELECT ProductID FROM Production.WorkOrder

• EXCEPT returns any distinct values from the query to the left of the EXCEPT operand that are not also returned from the right query

• INTERSECT returns any distinct values that are returned by both the query on the left and right sides of the INTERSECT operand

ProductID------------------429...(266 row(s) affected)

ProductID------------------429...(266 row(s) affected)

ProductID------------------3...(238 row(s) affected)

ProductID------------------3...(238 row(s) affected)

EXCEPT Example:

INTERSECT Example:

Result Sets

Identifying the Order of Precedence of UNION, EXCEPT, and INTERSECT

EXCEPT, INTERSECT, and UNION are evaluated in the context of the following precedence:

Expressions in parentheses 11

The INTERSECT operand 22

EXCEPT and UNION evaluated from Left to Right based on their position in the expression

33

Limiting Result Sets by Using the TOP and TABLESAMPLE Operators

• TOP and TABLESAMPLE limit the number of rows returned in a result set

SELECT TOP (15)FirstName, LastName

FROM Person.Person

SELECT TOP (15)FirstName, LastName

FROM Person.Person

SELECT FirstName, LastName

FROM Person.PersonTABLESAMPLE (1 PERCENT)

SELECT FirstName, LastName

FROM Person.PersonTABLESAMPLE (1 PERCENT)

FirstName LastName--------------------Syed AbbasCatherine Abel...(15 row(s) affected)

FirstName LastName--------------------Syed AbbasCatherine Abel...(15 row(s) affected)

FirstName LastName--------------------Eduardo BarnesEdward Barnes...(199 row(s) affected)

FirstName LastName--------------------Eduardo BarnesEdward Barnes...(199 row(s) affected)

TOP Example:

TABLESAMPLE Example:

Result Sets

Categorizing Statements That Limit Result Sets

• UNION

Combines the results of two or more SELECT statements into a single result set

• EXCEPT and INTERSECT

Compares the results of two or more SELECT statements and return distinct values

• TOP

Specifies that only the first set of rows will be returned from the query result

• TABLESAMPLE

Limits the number of rows returned from a table in the FROM clause to a sample number or PERCENT of rows

Demonstration: Combining and Limiting Result Sets

In this demonstration, you will see how to:

• Combine Result Sets

• Limit Result Sets using TABLESAMPLE

• Limit Result Sets using TOP

Lab: Joining Data from Multiple Tables

• Exercise 1: Querying Multiple Tables by Using Joins

• Exercise 2: Applying Joins for Typical Reporting Needs

• Exercise 3: Combining and Limiting Result Sets

Logon information

Virtual machine NY-SQL-01

User name Administrator

Password Pa$$w0rd

Estimated time: 60 minutes

Lab Scenario

•You are a database developer at Adventure Works. You have been asked by the various managers to prepare several reports for use in the quarterly financial statements being produced by the company. To create these reports you will use several different joins and join operators.

Lab Review

• What results did the Inner Join in Exercise 1 return?

• What results did the Left Outer Join and Right Outer Join in Exercise 1 return?

• Why was the ProductVendor table given two different table aliases in the FROM clause of Exercise 2?

• What would happen if we added an ORDER BY clause to the TOP select statement in Exercise 3?

Module Review and Takeaways

• Review Questions

• Best Practices