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Module 4:

Joining Data from MultipleTables

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Module 4: Joining Data from Multiple Tables

Querying Multiple Tables by Using Joins

Applying Joins for Typical Reporting Needs

Combining and Limiting Result Sets

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Lesson 1: Querying Multiple Tables by UsingJoins

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

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Fundamentals of Joins

Select Specific Columns from Multiple Tables

JOIN keyword specifies that tables are joined and howto join them

ON keyword specifies join condition

FROM first_tablejoin_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

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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

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Joining Data Using Inner Joins

SELECT e.LoginIDFROM HumanResources.Employee AS e

INNER JOIN Sales.SalesPerson AS sON e.BusinessEntityID = s.BusinessEntityID

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:

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Joining Data Using Outer Joins

SELECT p.Name, pr.ProductReviewIDFROM Production.Product pLEFT OUTER JOINProduction.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)

Example:

Result Set:

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Joining Data Using Cross Joins

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)

Example:

Result Set:

Use CROSS JOINs with caution if you do not need a trueCartesian Product

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Identifying the Potential Impact of a CartesianProduct

Is defined as all possible combinations of rows in alltables

A Cartesian Product:

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

Can result in huge result sets that take several hoursto complete!

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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

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Lesson 2: Applying Joins for Typical ReportingNeeds

Joining Three or More Tables

Joining a Table to Itself

Joining Tables by Using Non-Equi Joins

Joining Tables in a User-Defined Function

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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

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)

Result Set:

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Joining a Table to Itself

SELECT DISTINCT pv1.ProductID, pv1.BusinessEntityIDFROM Purchasing.ProductVendor pv1INNER JOIN Purchasing.ProductVendor pv2

ON pv1.ProductID = pv2.ProductIDAND pv1.BusinessEntityID pv2.BusinessEntityID

ORDER BY pv1.ProductID

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

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

Result Set:

Example:

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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.ProductSubcategoryIDAND 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)

Result Set:

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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 PJOIN Sales.SalesOrderDetail AS SD ONSD.ProductID = P.ProductID

JOIN Sales.SalesOrderHeader AS SH ONSH.SalesOrderID = SD.SalesOrderID

WHERE SH.CustomerID = @storeidGROUP 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

Example:

Result Set:

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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

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Lesson 3: Combining and Limiting Result Sets

Combining Result Sets by Using the UNION Operator

Limiting Result Sets by Using the EXCEPT and INTERSECTOperators

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

Limiting Result Sets by Using the TOP and TABLESAMPLEOperators

Categorizing Statements that Limit Result Sets

C bi i R lt S t b U i th UNION

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Combining Result Sets by Using the UNIONOperator

SELECT * FROM testa

UNION ALLSELECT * FROM testb;

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 toall queries in the union

Example:

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

Result Set:

Li iti R lt S t b U i th EXCEPT d

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Limiting Result Sets by Using the EXCEPT andINTERSECT Operators

SELECT ProductID

FROM Production.ProductEXCEPTSELECT ProductIDFROM Production.WorkOrder

SELECT ProductIDFROM Production.ProductINTERSECTSELECT ProductIDFROM Production.WorkOrder

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

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

ProductID

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

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

EXCEPT Example:

INTERSECT Example:

Result Sets

Id tif i th O d f P d f UNION

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

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

Expressions in parentheses1

The INTERSECT operand2

EXCEPT and UNION evaluated from Left to Right based on

their position in the expression3

Limiting Result Sets by Using the TOP and

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Limiting Result Sets by Using the TOP andTABLESAMPLE Operators

TOP and TABLESAMPLE limit the number of rows

returned in a result set

SELECT TOP (15)

FirstName, LastNameFROM Person.Person

SELECTFirstName, LastName

FROM Person.PersonTABLESAMPLE (1 PERCENT)

FirstName LastName--------------------Syed Abbas

Catherine Abel...(15 row(s) affected)

FirstName LastName

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

TOP Example:

TABLESAMPLE Example:

Result Sets

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Categorizing Statements That Limit Result Sets

UNION

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

EXCEPT and INTERSECT

Compares the results of two or more SELECT statements andreturn distinct values

TOP

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

TABLESAMPLE

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

Demonstration: Combining and Limiting Result

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Demonstration: Combining and Limiting ResultSets

In this demonstration, you will see how to:

Combine Result Sets

Limit Result Sets using TABLESAMPLE

Limit Result Sets using TOP

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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-01User name Administrator

Password Pa$$w0rd

Estimated time: 60 minutes

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Lab Scenario

You are a database developer at Adventure Works. You havebeen asked by the various managers to prepare several reports

for use in the quarterly financial statements being produced bythe company. To create these reports you will use severaldifferent joins and join operators.

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Lab Review

What results did the Inner Join in Exercise 1 return?

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

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

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

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Module Review and Takeaways

Review Questions

Best Practices