Introduction to SQL Server 2005/2008 and Transact SQL

Transcription

1 Introduction to SQL Server 2005/2008 and Transact SQL Week 3: The ins and outs of JOINS Can you relate? Steve Stedman - Instructor Steve@SteveStedman.com

2 This Weeks Overview Introduction to SQL Server and Transact SQL - Week 3 Review of Last Week Homework Review Querying Related Tables / Join Syntax Inner Joins Left / Right Outer Join Cross Joins Unions Sub-Queries

3 Last Weeks Review Introduction to SQL Server and Transact SQL - Week 2 Review of Last Week Homework Review AdventureWorks Database Diagram Simple Selects Simple Inserts Simple Updates Simple Delete Aggregating Data

4 Homework Review Reviewing homework from last week SQL Queries Reading Assignment "Professional SQL Server 2005" Chapter 6 or "Professional SQL Server 2008" Chapter 3

5 SSMS - Tip of the Week Visualizing Database Relationships With SSMS Database Diagrams you can see a visual representation of relationships Very useful on finding which tables are related to the table you are working with Demo... Add Employee, EmployeeDepartmentHistory, and Department

6 1. JOIN Syntax Querying Related Tables JOINs allow you to link data from two or more tables into a single query result set The JOIN is what makes a relational database system relational The JOIN combines the data from two or more tables

7 What is a JOIN A JOIN shows all rows from Table1 that match up with Table2 using the JOIN ON condition

8 Old Style JOIN Syntax A JOIN can be recognized in a SQL SELECT statement if it has more than one table after the FROM keyword Add a WHERE clause that links the tables Examples: SELECT c.firstname + ' ' + c.lastname, e.birthdate FROM HumanResources.Employee e, Person.Contact c WHERE e.contactid = c.contactid;

9 Specific JOIN Syntax A more acceptable JOIN syntax Updated syntax to create a JOIN between two tables use JOIN and ON keywords in the SELECT statement Examples: SELECT c.firstname + ' ' + c.lastname, e.birthdate FROM HumanResources.Employee e JOIN Person.Contact c ON e.contactid = c.contactid;

10 JOIN More than 2 tables A join can apply to 2 more more tables Add multiple JOIN and ON commands into the SELECT statement SELECT c.firstname + ' ' + c.lastname, e.birthdate, a.city, a.postalcode FROM HumanResources.Employee e JOIN Person.Contact c ON e.contactid = c.contactid JOIN HumanResources.EmployeeAddress ea ON e.employeeid = ea.employeeid JOIN Person.Address a ON ea.addressid = a.addressid;

11 JOIN Lab Project JOIN any 3 tables in the AdventureWorks database, pull in data from 2 or more of the tables in the JOIN

12 End of JOIN Syntax Any Questions Next Topic - INNER JOINS

13 2. INNER JOINS Specifying the type of JOIN Similar to the JOIN syntax Return only rows that match from both tables SELECT * FROM HumanResources.Employee E INNER JOIN HumanResources.EmployeeAddress as EA ON E.EmployeeId = EA.EmployeeId

14 JOIN vs INNER JOIN? A question from StackOverflow.com Both these JOINs will give me the same results: SELECT * FROM table JOIN othertable ON table.id = othertable.fk SELECT * FROM table INNER JOIN othertable ON table.id = othertable.fk Is there any difference between the statements in performance or otherwise? Does it differ between different SQL implementations?

15 INNER JOINS vs JOIN Whats the difference? They function the same INNER JOIN can be a bit more clear to read, especially if your query has other join types (e.g. LEFT or RIGHT) included in it

16 End of INNER JOINS Any Questions Next Topic - OUTER JOINS

17 3. OUTER JOINS Returns rows with matching data, as well as rows with nonmatching (null) data LEFT OUTER JOIN All the rows from the LEFT table RIGHT OUTER JOIN All the rows from the RIGHT table FULL OUTER JOIN All the rows from both the LEFT and RIGHT

18 LEFT OUTER JOIN The left outer join retrieves records from both tables, retrieving all the records from the left table and any records from the right table where the condition values match

19 LEFT OUTER JOIN Examples The following left outer join shows all products LEFT OUTER JOINed to orders Examples: SELECT p.productid, o.productid, o.salesorderid FROM Production.Product p LEFT OUTER JOIN Sales.SalesOrderDetail o ON p.productid = o.productid ORDER BY o.salesorderid ASC;

20 RIGHT OUTER JOIN The right outer join is similar to the left outer join in that it retrieves all the records from one side of the relationship, but this time it's the right table. Only records where the condition values match are retrieved from the left

21 RIGHT OUTER JOIN Sample Code The following RIGHT OUTER JOIN will show all sales people who are not associated with a sales territory Examples: SELECT st.name AS Territory, sp.salespersonid FROM Sales.SalesTerritory st RIGHT OUTER JOIN Sales.SalesPerson sp ON st.territoryid = sp.territoryid WHERE st.name is NULL;

22 FULL OUTER JOIN Show everything from Table 1 plus everything from table 2, match them up if there is a match on the join condition, otherwise just show nulls

23 OUTER JOINS Lab Lab Project Use a RIGHT OUTER JOIN to show products that don't have any orders Use a LEFT OUTER JOIN to show territories that don't have any salespeople associated with them

24 End of Topic OUTER JOINS Any Questions 5 Minute Break Next Topic - CROSS JOINS

25 4. CROSS JOINS A cross JOIN devoid of a WHERE clause produces the Cartesian product of the tables involved in the JOIN

26 CROSS JOINS Syntax This JOIN has a slightly different format in that it does not have a ON clause Also known as a Cartesian JOIN because it creates the cartesian production of two tables SELECT p.salespersonid, t.name AS Territory FROM Sales.SalesPerson p CROSS JOIN Sales.SalesTerritory t ORDER BY p.salespersonid;

27 CROSS JOIN result set The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table.

28 CROSS JOINS Lab Project Create a CROSS JOIN Query with 2 tables in the AdventureWorks database

29 End of CROSS JOINS Any Questions Next Topic - Self JOIN

30 5. Self JOINs Joining a table with itself A self JOIN is where a table is joined with itself, using any of the other JOIN types Self JOINs can simplify many SQL queries that make multiple references to the same table A Self JOIN can be of any type (INNER, OUTER, FULL, LEFT, RIGHT), as long as the joined tables are the same

31 Self JOIN Example The following table is a Self JOIN which JOINs Employee to itself to show the relationship between employees and managers Examples: SELECT m.loginid as Manager, e.loginid as Employee FROM HumanResources.Employee e INNER JOIN HumanResources.Employee m ON e.managerid = m.employeeid;

32 SELF JOINS Lab Lab Project Using the Employee table in AdventureWorks, write a query that shows all employees login, along with their managers login.

33 End of Self JOINS Any Questions Next Topic - UNIONS

34 6. UNIONS Merge the results from any combination of two or more queries or SELECT statements into a single result set All queries in a UNION must request the same number of fields By default, a UNION only returns unique records UNION ALL includes duplicates, UNION does not include duplicates

35 UNION Samples The results from one query are combined with the results from another query eliminating duplicates Example: SELECT * FROM HumanResources.Employee WHERE Title LIKE '%assistant%' UNION SELECT * FROM HumanResources.Employee WHERE Title LIKE '%vice president%';

36 End of UNIONS Any Questions Next Topic - Sub-Queries

37 7. Sub-Queries A sub query adds another SELECT statement into your query Sub-queries can be used in different part of the SELECT statement SELECT column list FROM WHERE HAVING

38 Correlated and Non-Correlated Two types of Sub-Queries A correlated subquery is an inner subquery which is referenced by the main outer query such that the inner query is considered as being executed repeatedly A noncorrelated subquery is subquery that is independent of the outer query and it can executed on its own without relying on main outer query

39 Sub-Query in the column list A Sub-Query in the column list is run for every row in the result set The sub-query produces a single value which is placed into the result set Example: SELECT Ord.SalesOrderID, Ord.OrderDate, (SELECT MAX(OrdDet.UnitPrice) FROM Sales.SalesOrderDetail AS OrdDet WHERE Ord.SalesOrderID = OrdDet.SalesOrderID) AS MaxUnitPrice FROM Sales.SalesOrderHeader AS Ord

40 Sub-Query in the FROM clause JOINing to a Sub-Query The Sub-query in the FROM clause acts like another table that the query is being JOINed to Use aliasing to name the sub-query like a table Examples: SELECT p.* FROM Production.Product p, (SELECT ProductSubcategoryID FROM Production.Product WHERE Color = 'Red') as t WHERE p.productsubcategoryid = t.productsubcategoryid

41 Sub-Query in the WHERE clause Filtering results on a the results from a subquery Used to compare a column to a specific value that can be found with the subquery Examples: SELECT Name, ListPrice FROM Production.Product WHERE ListPrice = (SELECT ListPrice FROM Production.Product WHERE Name = 'Road-750 Black, 58')

42 More Sub-Query in the WHERE clause Using the IN statement The IN comparison checks to see if a value is in a list of results Examples: SELECT Name FROM Production.Product WHERE ProductSubcategoryID IN (SELECT ProductSubcategoryID FROM Production.ProductSubcategory WHERE Name = 'Wheels')

43 Sub-query in the HAVING clause Filter group data on the results of a sub-query Similar to the WHERE clause sub-queries but the check is applied to the GROUP BY Examples: SELECT e.managerid, AVG(e.VacationHours) FROM HumanResources.Employee e GROUP BY e.managerid HAVING AVG(e.VacationHours) > (SELECT AVG(VacationHours) FROM HumanResources.Employee)

44 Lab... Sub-Queries Lab Project Using a subquery, show all employees who have ever worked in a department with sales in the department name You will need to use data from the following tables HumanResources.EmployeeDepartmentHistory HumanResources.Department HumanResources.Employee

45 End of Sub-Queries Any Questions

46 This Saturday Technology Theme Class 4 Overview of database design 1st, 2nd and 3rd normal form. Creating Tables Creating Relationship Implementing Constraints Class 5 SQL Server Reporting Services SSRS Reporting Matrix Reporting Advanced Reporting Course Review

47 Homework Introduction to SQL Server 2005/2008 and Transact SQL Homework for next week Read "Professional SQL Server 2005" Chapter 7 and 17 or "Professional SQL Server 2008" Chapter 5 and 14

48 This Weeks Review Introduction to SQL Server and Transact SQL - Week 3 Review of Last Week Homework Review Querying Related Tables / Join Syntax Inner Joins Left / Right Outer Join Cross Joins Unions Sub-Queries Lab: Experimenting with the output from different types of joins on the same data

49 Any Questions? End of Class