20190310 - SQL Course - JOIN
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The document summarizes the 16th meeting of Module 3 on JOIN. The agenda includes a review of sets theory, relational databases, and JOIN syntax in SQL. It then covers the different types of JOINs - INNER JOIN, OUTER JOIN (LEFT, RIGHT, FULL), CROSS JOIN, and SELF JOIN. Examples are provided for INNER JOIN, OUTER JOIN, and CROSS JOIN.
![Inner Joins
• Return only rows where a match is found in both input tables
• Match rows based on attributes supplied in predicate
• If join predicate operator is =, also known as equi-join
Employee SalesOrder
Set returned
by inner join
SELECT emp.FirstName, ord.Amount
FROM HR.Employee AS emp
[INNER] JOIN Sales.SalesOrder AS ord
ON emp.EmployeeID = ord.EmployeeID](https://image.slidesharecdn.com/module-3-190319054325/85/20190310-SQL-Course-JOIN-10-320.jpg)
![Outer Joins
• Return all rows from one table and any matching
rows from second table
• One table’s rows are “preserved”
• Designated with LEFT, RIGHT, FULL keyword
• All rows from preserved table output to result set
• Matches from other table retrieved
• Additional rows added to results for non-
matched rows
• NULLs added in places where attributes do not match
• Example: Return all employees and for those
who have taken orders, return the order
amount. Employees without matching orders
will display NULL for order amount.
Employee SalesOrder
Set returned
by left outer
join
SELECT emp.FirstName, ord.Amount
FROM HR.Employee AS emp
LEFT [OUTER] JOIN Sales.SalesOrder AS ord
ON emp.EmployeeID = ord.EmployeeID;](https://image.slidesharecdn.com/module-3-190319054325/85/20190310-SQL-Course-JOIN-11-320.jpg)
20190310 - SQL Course - JOIN
- 1. 16th Meeting Module 3 – JOIN 9:00PM – 10:30 PM – March 10th, 2019 Lai Trung Minh Duc | DucLTM@outlook.com Microsoft Student Partners Vietnam | Analytics Vietnam Community Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 1
- 2. Agenda • Sets Theory review • Relational Database review • JOIN Syntax Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 2
- 3. Hello World, Lai Trung Minh Duc Former External Economics student @ FTU Former Solution Architect @ Savills Vietnam Information Assurance student @ FPT Tech-writer @ Duck’s Tech Zone Solution Architect @ Pizitech LTD. Tech-trainer @ Microsoft Student Partners Vietnam Tech-love: ASPNET Core, Python, Angular, ReactJS, Docker, SQL Interests: Data Visualization, Data Analytics, Finance, Marketing, HR Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 3
- 4. Knowledge Review – Sets Theory Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 4
- 5. Knowledge Review – Relational Database Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 5
- 6. Knowledge Review – Relational Database Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 6
- 7. JOIN in SQL • INNER JOIN • OUTER JOIN • LEFT JOIN • RIGHT JOIN • FULL JOIN • CROSS JOIN • SELF JOIN Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 7
- 8. Knowledge Review – JOIN in SQL Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 8 Work with specified columns (conditional) JOIN… ON <condition1> AND <condition2> OR <condition3>
- 9. Join Syntax • ANSI SQL-92 • Tables joined by JOIN operator in FROM Clause • Preferred syntax • ANSI SQL-89 • Tables joined by commas in FROM Clause • Not recommended: Accidental Cartesian products! SELECT ... FROM Table1 JOIN Table2 ON <on_predicate>; SELECT ... FROM Table1, Table2 WHERE <where_predicate>;
- 10. Inner Joins • Return only rows where a match is found in both input tables • Match rows based on attributes supplied in predicate • If join predicate operator is =, also known as equi-join Employee SalesOrder Set returned by inner join SELECT emp.FirstName, ord.Amount FROM HR.Employee AS emp [INNER] JOIN Sales.SalesOrder AS ord ON emp.EmployeeID = ord.EmployeeID
- 11. Outer Joins • Return all rows from one table and any matching rows from second table • One table’s rows are “preserved” • Designated with LEFT, RIGHT, FULL keyword • All rows from preserved table output to result set • Matches from other table retrieved • Additional rows added to results for non- matched rows • NULLs added in places where attributes do not match • Example: Return all employees and for those who have taken orders, return the order amount. Employees without matching orders will display NULL for order amount. Employee SalesOrder Set returned by left outer join SELECT emp.FirstName, ord.Amount FROM HR.Employee AS emp LEFT [OUTER] JOIN Sales.SalesOrder AS ord ON emp.EmployeeID = ord.EmployeeID;
- 12. Cross Joins • Combine each row from first table with each row from second table • All possible combinations output • Logical foundation for inner and outer joins • Inner join starts with Cartesian product, adds filter • Outer join takes Cartesian output, filtered, adds back non-matching rows (with NULL placeholders) • Due to Cartesian product output, not typically a desired form of join • Some useful exceptions: • Table of numbers, generating data for testing Employee EmployeeID FirstName 1 Dan 2 Aisha Product ProductID Name 1 Widget 2 Gizmo Result FirstName Name Dan Widget Dan Gizmo Aisha Widget Aisha Gizmo SELECT emp.FirstName, prd.Name FROM HR.Employee AS emp CROSS JOIN Production.Product AS prd;
- 13. Knowledge Sharing Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 13 Work with all columns (non- conditional)
- 14. Notes • ER Diagram Lai Trung Minh Duc | March 2019 | DucLTM@outlook.com 14