SQL Joins using venn diagrams

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SQL JOINS using Venn diagrams

What is Join? A relational operation that causes two or more tables with a common domain to be

combined into a single table or view SQL joins creates a set of row in a temporary table

SQL Joins

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EQUI JOINS EQUI JOINS is a simple SQL join. Uses equals to(=) sign as the comparison operator for the condition.

NON EQUI JOINS NON EQUI JOINS uses comparison operator other than the equal sign. The operator used like >, <, >=, <= with the condition.

Types of SQL Joins




Types of SQL EQUI JOIN

INNER JOIN It returns on matched row from the participating table. Match happened only at the key record of the participating table.

OUTER JOIN Returns all rows from one table and matching row from the secondary table. And the comparison columns should be equal in both the table.




Lists of SQL JOINS

INNER JOIN

LEFT JOIN or LEFT OUTER JOIN

RIGHT JOIN or RIGHT OUTER JOIN

FULL OUTER JOIN




INNER JOIN

The INNER JOIN selects all rows from both participating tables as long as there is a match between the columns.

An SQL INNER JOIN is same as JOIN clause, combining rows from two or more tables.




Example : INNER JOIN

ID Address1 Delhi

2 Mumbai

3 Chennai

ID Name1 Divyesh

2 Astaj

3 Nishith

4 Aakash

Table : Employee Table : Employee_City




Example : INNER JOIN (Cont.)

SELECT * FROM Employee INNER JOIN Employee_City on Employee.ID = Employee_city.ID;

OUTPUT

QUERY

ID Name ID Address

1 Divyesh 1 Delhi

2 Astaj 2 Mumbai

3 Nishith 3 ChennaiEmployee Employee_City




LEFT JOIN or LEFT OUTER JOIN

The LEFT OUTER 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.




Example : LEFT OUTER JOIN or LEFT JOIN

ID Address1 Delhi

2 Mumbai

3 Chennai

5 Ahmedabad

ID Name1 Divyesh

2 Astaj

3 Nishith

4 Aakash





SELECT * FROM Employee LEFT JOIN Employee_City on Employee.ID = Employee_City.ID;

Example : LEFT OUTER JOIN or LEFT JOIN(Cont.)

OUTPUT

QUERY

ID Name ID Address

1 Divyesh 1 Delhi

2 Astaj 2 Mumbai

3 Nishith 3 Chennai

4 Aakash NULL NULL

Employee Employee_City




SELECT * FROM Employee LEFT JOIN Employee_City on Employee.ID = Employee_City.ID Where Employee_City.ID is NULL;

Example : LEFT OUTER JOIN or LEFT JOIN(Cont.)

OUTPUT

QUERY


ID Name ID Address

4 Aakash NULL NULL




RIGHT JOIN or RIGHT OUTER JOIN

The RIGHT OUTER 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 after the JOIN clause.




Example : RIGHT OUTER JOIN or RIGHT JOIN

ID Address1 Delhi

2 Mumbai

3 Chennai

5 Ahmedabad

ID Name1 Divyesh

2 Astaj

3 Nishith

4 Aakash





SELECT * FROM Employee RIGHT JOIN Employee_City on Employee.ID = Employee_City.ID;

Example : RIGHT OUTER JOIN or RIGHT JOIN(Cont.)

OUTPUT

QUERY

ID Name ID Address1 Divyesh 1 Delhi

2 Astaj 2 Mumbai

3 Nishith 3 Chennai

null null 5 Ahmedabad





SELECT * FROM Employee RIGHT JOIN Employee_City OnEmployee.ID= Employee_City.IDWhere Employee.ID is NULL;

Example : RIGHT OUTER JOIN or RIGHT JOIN(Cont.)

OUTPUT

QUERY


ID Name ID Address

NULL NULL 5 Ahmedabad




FULL OUTER JOIN

Combines the result of both left outer and right outer join

Returns all match and unmatched rows.

Includes tables on both side of join clause




Example : FULL OUTER JOIN

ID Address1 Delhi

2 Mumbai

3 Chennai

5 Ahmedabad

ID Name1 Divyesh

2 Astaj

3 Nishith

4 Aakash





SELECT * FROM Employee FULL OUTER JOIN Employee_City on Employee.ID = Employee_City.ID;

Example : FULL OUTER JOIN(Cont.)

OUTPUT

QUERY

ID Name ID Address

1 Divyesh 1 Delhi

2 Astaj 2 Mumbai

3 Nishith 3 Chennai

4 Aakash null null






select * from Employee FULL OUTER JOIN Employee_Cityon Employee.ID = Employee_City.IDWHERE Employee.ID is NULL orEmployee_City.ID is NULL

Example : FULL OUTER JOIN(Cont.)

OUTPUT

QUERY


ID Name ID Address

4 Aakash null null



