Joins In SQL Server 2017

Introduction

 
In this article, I am going to explain about joins and types of joins with examples. Here we will be using SQL Server 2017 or you can use SQL Server 2008 or above.
 
Definition
 
Joins are used to fetch/retrieve data from two or more related tables from a data base. In general, tables are related to each other using foreign key constraints.
 

Types of Joins

 
There are four types of joins in SQL Server.
  • Inner Join
  • Outer Join
  • Cross Join
  • Self Join
Again, Outer Joins are divided into three types.
  • Left Join or Left Outer Join
  • Right Join or Right Outer Join
  • Full Join or Full Outer Join
Now, I am going to explain different types of joins with examples and the differences between them.
 
Prerequisites
 
SQL Server 2017 or you can use SQL server 2008 or above version.
 
Now, first we will create a Database and two tables to apply the joins for understanding.
 

Creating Database and Two Tables

 
Step 1 - Create a Database
 
Open your SQL Server and use the following script to create the “chittadb” Database.
  1. Create database chittadb   
Now, select the script query then press F5 or click on Execute button to execute the above script.
 
You should see a message, “Command(s) completed successfully.” This means your new database has been created.
 
Step 2 - Create first table
 
Open your SQL Server and use the following script to create table “tbl_Department”.
  1. create table tbl_Department  
  2. (  
  3.    DeptId int primary key not null identity(1,1),  
  4.    DeptName nvarchar(50),  
  5.    DeptHead nvarchar(50),  
  6.    Location nvarchar(100)  
  7. )  
Execute the above query to create “tbl_Department “.
 
You should see a message, “Command(s) completed successfully.”
 
Now, data is inserted into the table.
  1. Insert into tbl_Department values ( 'IT''Chitta''Chennai')  
  2. Insert into tbl_Department values ( 'Payroll''Akhil''Odisha')  
  3. Insert into tbl_Department values ( 'HR''Ram''Pune')  
  4. Insert into tbl_Department values ( 'Timesheet''Kannan''chennai')  
Execute the above query, you should see a message, “Command(s) completed successfully.”
 
Now retrieve all data from “tbl_Department” table.
  1. select * from tbl_Department  
output
 
Joins In SQL Server
 
Step 3 - Create second table
 
Open your SQL Server and use the following script to create table “tbl_Employee”.
  1. Create table tbl_Employee  
  2. (  
  3.      EmpID int primary key not null identity(1,1),  
  4.      Name nvarchar(50),  
  5.      Gender nvarchar(50),  
  6.      country nvarchar(20),  
  7.      Salary int,  
  8.      DepartmentId int foreign key references tbl_Department(DeptId)  
  9. )  
Execute the above query to create “tbl_Employee “.
 
You should see a message, “Command(s) completed successfully.”
 
Now, data is inserted into the table.
  1. Insert into tbl_Employee values ( 'Jitu''Male','India',4000, 1)  
  2. Insert into tbl_Employee values ( 'Rani''Female','India', 5000, 3)  
  3. Insert into tbl_Employee values ( 'Rohit''Male','India', 5500, 1)  
  4. Insert into tbl_Employee values ( 'Dibas''Male','India', 6500, 2)  
  5. Insert into tbl_Employee values ( 'Gajendra''Male','India', 3800, 2)  
  6. Insert into tbl_Employee values ( 'Raja''Male','India', 9000, 1)  
  7. Insert into tbl_Employee values ( 'Jeni''Female','India', 5800, 3)  
  8. Insert into tbl_Employee values ( 'Chandin''Female','India', 8500, 1)  
  9. Insert into tbl_Employee values ( 'pintu''Male','India', 9500, NULL)  
  10. Insert into tbl_Employee values ( 'Subrat''Male','India', 9800, NULL)  
Execute the above query, you should see a message, “Command(s) completed successfully.”
 
Now retrieve all data from “tbl_Employee” table.
  1. select * from tbl_Employee  
output
 
Joins In SQL Server
 
General Formula for Joins,
  1. SELECT      ColumnList (whatever column you want to display)   
  2. FROM           LeftTableName   
  3. JOIN_TYPE  RightTableName   
  4. ON                 JoinCondition  

INNER JOIN

 
Inner join returns only the matching rows between both the tables; non-matching rows are eliminated.
 
Example
 
Write a query to retrieve Name, Gender, Country, Salary and DeptName from tbl_Employee and tbl_Department table.
 
INNER JOIN Query
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. INNER JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
OR
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3.  JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
Note
JOIN or INNER JOIN  are the same. It's always better to use INNER JOIN.
 
OR
  1. select emp.Name,emp.Gender,emp.country,emp.Salary,dept.DeptName   
  2.     from tbl_Employee emp   
  3.     inner join tbl_Department dept  
  4.     on emp.DepartmentId=dept.DeptId  
OutPut
 
Joins In SQL Server
 

LEFT JOIN or LEFT OUTER JOIN

 
Left Join or Left Outer Join returns only the matching rows between both the tables, plus non-matching rows from the left table.
 
Example
 
Write a query to retrieve Name, Gender, Country, Salary and DeptName from tbl_Employee and tbl_Department table.
 
LEFT JOIN or LEFT OUTER JOINQuery,
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. LEFT OUTER JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
OR
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. LEFT JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
Note
You can use, LEFT JOIN or LEFT OUTER JOIN. OUTER keyword is optional.
 
OR
  1. select emp.Name,emp.Gender,emp.country,emp.Salary,dept.DeptName   
  2.     from tbl_Employee emp   
  3.     LEFT JOIN tbl_Department dept  
  4.     on emp.DepartmentId=dept.DeptId  
OutPut
 
Joins In SQL Server
 

RIGHT JOIN or RIGHT OUTER JOIN

 
Right Join or Right Outer Join returns only the matching rows between both the tables, plus non-matching rows from the right table.
 
Example
 
Write a query to retrieve Name, Gender, Country, Salary and DeptName from tbl_Employee and tbl_Department table.
 
RIGHT JOIN or RIGHT OUTER JOIN Query,
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. RIGHT JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
OR
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. RIGHT OUTER JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
Note
You can use, RIGHT JOIN or RIGHT OUTER JOIN. OUTER keyword is optional.

OR
  1. select emp.Name,emp.Gender,emp.country,emp.Salary,dept.DeptName   
  2.     from tbl_Employee emp   
  3.     RIGHT JOIN tbl_Department dept  
  4.     on emp.DepartmentId=dept.DeptId  
OutPut
 
Joins In SQL Server
 

FULL JOIN or FULL OUTER JOIN

 
Full Join or Full Outer Join returns all rows from both the tables (left & right tables), including non-matching rows from both the tables.
 
Example
 
Write a query to retrieve Name, Gender, Country, Salary and DeptName from tbl_Employee and tbl_Department table.
 
FULL JOIN or FULL OUTER JOIN Query,
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. FULL OUTER JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
OR
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. FULL JOIN tbl_Department  
  4. ON tbl_Employee.DepartmentId = tbl_Department.DeptId  
Note
You can use, FULL JOIN or FULL OUTER JOIN. OUTER keyword is optional.
 
OR
  1. select emp.Name,emp.Gender,emp.country,emp.Salary,dept.DeptName   
  2.     from tbl_Employee emp   
  3.     FULL JOIN tbl_Department dept  
  4.     on emp.DepartmentId=dept.DeptId  
OutPut
 
Joins In SQL Server
 

CROSS JOIN


CROSS JOIN, produces the Cartesian product of the 2 tables.
 
For example, in the tbl_Employee table we have 10 rows and in the tbl_Department table we have 4 rows. So, a cross join between these 2 tables produces 40 rows. Cross Join shouldn't have ON clause. 
 
Example
 
Write a query, to retrieve Name, Gender, Country, Salary and DeptName from tbl_Employee and tbl_Department table.

CROSS JOIN Query
  1. SELECT Name, Gender,country, Salary, DeptName   
  2. FROM tbl_Employee  
  3. CROSS JOIN tbl_Department  
OR
  1. select emp.Name,emp.Gender,emp.country,emp.Salary,dept.DeptName   
  2.     from tbl_Employee emp   
  3.     cross JOIN tbl_Department dept  
OutPut
 
Joins In SQL Server
 

Conclusion

 
In this article, I explained joins in SQL Server with examples. I hope this article has helped you to understand this topic. Post your valuable feedback in the comments section.