SQL for Beginners Series - Session 12

JOINS in SQL

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Exercise:

For this exercise, we are considering 2 tables 

    tblEmployee

    tblDept

Deptid is the joining column between these 2 tables. 

In Relational databases, all the data is not loaded in a single table, but it will be loaded in multiple tables and those tables will have relations. This process of reducing the redundancy is called Normalization.

These tables can be joined using JOINS in SQL.

There are 4 types of join in SQL

INNER JOIN or JOIN

LEFT JOIN or LEFT OUTER JOIN 

RIGHT JOIN or RIGHT OUTER JOIN

FULL JOIN or FULL OUTER JOIN

Scripts Used:

CREATE TABLE tblEmployee (Empid INT NULL

,EmpName Varchar(50) NULL

,Deptid INT NULL

)

CREATE TABLE tblDept (Deptid INT NULL

                     ,DeptName Varchar(50) NULL

                     )

INSERT tblEmployee Values (1,'Emp5',NULL), (2,'Emp2',2),(3,'Emp3',3)

INSERT tblDept Values  (1, 'HR'),(2, 'Finance'),(3,'IT'),(NULL,'Sales')

--INNER JOIN – Returns the common records between two tables

--LEFT JOIN -  Returns all the rows from Left table and matching rows between two tables

--LEFT JOIN = INNER JOIN + Records from Left table

--RIGHT JOIN – Returns all the rows from Left table and matching rows 

--between two tables

--RIGHT JOIN = INNER JOIN + Records from Right table

--FULL JOIN -  Returns all the rows from two tables

 

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