Complete SQL joins by Muhammad Noman

2. SQL JOINs
DATABASE APPLICATIONS CS-320

3. What is SQL Joins
❖ JOIN clause combines rows from two or more tables.
❖ creates a set of rows in a temporary table.

4. WHY SQL JOINS?

5. Types of SQL JOIN
• INNER JOIN
• OUTER JOIN

6. Types of Inner JOIN
• NON EQUI JOIN
• EQUI JOIN
• Natural JOIN

7. NON EQUI JOIN
• Syntax…
• SELECT *
• FROM Table_name1, Table_name2
• Where Table_name1.column [< | > |>= |<= ] Table_name2.column ;

8. Types of Outer Join
• LEFT JOIN OR LEFT OUTER JOIN
• RIGHT JOIN OR RIGHT OUTER JOIN
• FULL OUTER JOIN

9. List of SQL JOINS
• INNER JOIN
• LEFT JOIN OR LEFT OUTER JOIN
• RIGHT JOIN OR RIGHT OUTER JOIN
• FULL OUTER JOIN
• NATURAL JOIN
• CROSS JOIN
• SELF JOIN

10. INNER JOIN
• Matching column values

11. Syntax
• SELECT columnlist
• FROM lefttable
• Join-type right table
• ON (join_Condition)

12. Example
SELECT employee.lastName,employee
departmentID,department.DepartmentNa
me
FROM employee INNER JOIN Department
ON employee .DepartmentID =
department.DepartmentID;
Employee.
LastName
Employee.D
epartmentI
D
Department
.Departmen
tName
Robinson 34 Clerical
Jones 33 Engineering
Smith 34 Clerical
Heisenberg 33 Engineering
Rafferty 31 Sales

13. IN MYSQL
• SELECT A.`first_name` , A.`last_name` , B.`title`
• FROM `members`AS A
• INNER JOIN `movies` AS B ON B.`id` = A.`movie_id

14. Inner Join (simple join) in Oracle
• Syntax....
• SELECT columns
• FROM table1
• INNER JOIN table2
• ON table1.column =
table2.column;

15. Example
supplier_id supplier_name
10000 IBM
10001 Hewlett Packard
10002 Microsoft
10003 NVIDIA
order_id supplier_id order_date
500125 10000 2003/05/12
500126 10001 2003/05/13
500127 10004 2003/05/14

16. Example
supplier_id name order_date
10000 IBM 2003/05/12
10001 Hewlett
Packard
2003/05/13
• SELECT suppliers.supplier_id,
suppliers.supplier_name,
orders.order_date
• FROM suppliers
• INNER JOIN orders
• ON suppliers.supplier_id =
orders.supplier_id;

17. LEFT JOIN
• The SQL LEFT JOIN, joins two tables and fetches rows based on a condition,
which are matching in both the tables.
• The unmatched rows will also be available from the table before the JOIN
clause.

18. Example
SELECT *
FROM employee
LEFT OUTER JOIN Department
ON employee .DepartmentID =
department.DepartmentID;
Employee.La
stName
Employee.Depar
tmentID
Department.De
partmentName
Department.De
partmentID
Jones 33 Engineering 33
Rafferty 31 Sales 31
Robinson 34 Clerical 34
Smith 34 Clerical 34
Williams NULL NULL NULL
Heisenberg 33 Engineering 33

19. RIGHT JOIN OR RIGHT OUTER JOIN
• A RIGHT JOIN is similar to the Left Join only the roles are reversed.
Basically you return all rows from the right table and the matched
rows from the left table.

20. Example
SELECT *
FROM employee
RIGHT OUTER JOIN Department
ON employee .DepartmentID =
department.DepartmentID;
Employee.L
astName
Employee.D
epartmentI
D
Department.
Department
Name
Department.
Department
ID
Smith 34 Clerical 34
Jones 33 Engineering 33
Robinson 34 Clerical 34
Heisenberg 33 Engineering 33
Rafferty 31 Sales 31
NULL NULL Marketing 35

21. Right Join (Right Outer join) in Oracle
• Syntax....
• SELECT columns
• FROM table1
• RIGHT [OUTER] JOIN table2
• ON table1.column =
table2.column;

22. JOINS and the WHERE Clause
• The WHERE clause specifies the relationship between tables listed
in the FROM clause.
• It also restricts the rows displayed in the result table.
• The most commonly used JOIN operator is the "equal" (=) sign.

23. JOIN Three Tables
• SELECT Orders.OrderID, Customers.CustomerName,
Shippers.ShipperName
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID =
Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);

24. Full outer join
• Reverse to Inner join
• LEFT and RIGHT JOIN at the
same time
• Full join can return very large
datasets.

25. Example
SELECT *
FROM employee
FULL OUTER JOIN Department
ON employee .DepartmentID =
department.DepartmentID;
Employee.L
astName
Employee.D
epartmentID
Department.
Department
Name
Department.
DepartmentI
D
Smith 34 Clerical 34
Jones 33 Engineering 33
Robinson 34 Clerical 34
Williams NULL NULL NULL
Heisenberg 33 Engineering 33
Rafferty 31 Sales 31
NULL NULL Marketing 35

26. Full Join (Full Outer Join) in Oracle
• Synatx:
• SELECT columns
• FROM table1
• FULL [OUTER] JOIN table2
• ON table1.column =
table2.column;

27. NATURAL JOIN
• The SQL NATURAL JOIN is a type of EQUI JOIN and is structured in
such a way that, columns with same name of associate tables will
appear once only.
• The columns must be the same data type.

28. Example
• SELECT *
• FROM Foods
NATURAL JOIN Company;

29. "ON" and "USING" clauses
• In above JOIN query examples, we have used ON clause to match
the records between table.
• USING clause can also be used for the same purpose. The
difference with USING is it needs to have identical names for
matched columns in both tables.

30. OTHERs…
• Apart from using ON and USING with JOINs you can use many
other MySQL clauses like GROUP BY, WHERE and even functions
like SUM, AVG, etc.

31. CROSS JOIN
• The SQL CROSS JOIN produces a result set which is the number of
rows in the first table multiplied by the number of rows in the
second table, if no WHERE clause is used along with CROSS JOIN.

32. CROSS JOIN

33. Example
SELECT *
FROM Employee
Cross JOIN Department
Employee.L
astName
Employee.D
epartmentID
Department.
Department
Name
Department.
DepartmentI
D
Rafferty 31 Sales 31
Jones 33 Sales 31
Heisenberg 33 Sales 31
Smith 34 Sales 31
Robinson 34 Sales 31
Williams NULL Sales 31

34. Syntax in Mysql workbench
• SELECT *
• FROM `movies`
CROSS JOIN `members’ ;

35. SELF JOIN
• A self-join is joining a table to
itself.

36. Example
Employe
eID
LastNam
e
Employe
eID
LastNam
e
Country
123 Rafferty 124 Jones Australia
123 Rafferty 145
Heisenb
erg
Australia
124 Jones 145
Heisenb
erg
Australia
305 Smith 306 Williams Germany
SELECT F.EmployeeID,
F.LastName, S.EmployeeID,
S.LastName, F.Country
FROM Employee F INNER
JOIN Employee S ON F.C
ountry = S.Country WHERE
F.EmployeeID < S.EmployeeID
ORDER BY F.EmployeeID,
S.EmployeeID;

37. POINT TO BE NOTED
• MySQL can achieve better performance with JOINs as it can use
Indexing. Further it requires more data manipulations in
application end also.

38. BASIC JOIN’s

39. Advanced Or Intelligent JOIN’s

40. SQL JOIN RFEFRENTIAL Integrity
• RI is a DB concept that is used to build and maintain logical
relationships between tables to avoid logical corruption of data
• Important part of RDBMS.

41. SUMMARY

42. Summary
• combine data from more than one table into a single result set.
• better performance compared to sub queries
• INNER JOINS only return rows that meet the given criteria.
• OUTER JOINS can also return rows where no matches have been
found. The unmatched rows are returned with the NULL keyword.
• The major JOIN types include Inner, Left Outer, Right Outer, Cross
JOINS etc.
• The frequently used clause in JOIN operations is "ON". "USING"
clause requires that matching columns be of the same name.
• JOINS can also be used in other clauses such as GROUP BY, WHERE,
SUB QUERIES, AGGREGATE FUNCTIONS etc.

43. Queries
• Suppose there are two tables category and product.Both table
contains category_id. We want to fetch the records where both
tables contain same category_id .
• In Emp table there are two columns empno and mgr. Fetch the
records where empno and mgr are same.
• Retrieve each employee who is in a department and each
department that has an employee and also each employee who
is not part of a department and each department which doesn't
have an employee.

44. Queries
• Write a query in SQL to display the first name, last name,
department number and department name, for all employees for
departments 80 or 40.
• Write a query in SQL to display all departments including those
where does not have any employee.
• Write a query in SQL to display the first name of all employees and
the first name of their manager including those who does not
working under any manager.

45. Query