Joins in SQL Server 2012

Introduction

 

In this article I describe joins, types of joins, Inner Joins, Left Outer Joins, Right Outer Joins, Full Outer Joins, Cross Joins and Self Joins with examples.

 

Joins

 

Joins are used to relate one or more tables in SQL Server. Joins are a part of a SQL Statement that retrieves rows from a table or tables according to specified conditions.

 

Types of Joins 

1. Inner Join
2. Outer Join
3. Cross Join
4. Self Join

First we create two tables on which we apply the joins.

 

Creation of the first table is as

create table emp(empId int, empName varchar(15))

Insertion of data into the table

insert into emp
select 1,'deepak'union all
select 2,'Arora'union all
Select 3,'raj'union all
select 4,'Mahi'union all
select 5,'daljeet'union all
select 6,'kiran'

Output

select * from emp

 

Creation of second table

create table emp_add(empId int, empAdd varchar(25))

insertion of data

select 1,'Lakser'union all
select 2,'haridwar'union all
select 3,'usa'union all
select 7,'canada'union all
select 8,'punjab'union all
select 9,'Chandigarh'

Output

select * from emp_add

Inner Join

 

It return all the Rows that satisfy the join Condition. Inner join produces records that match in Tables.

 

select e.empId,e.empName,e1.empAdd from emp e inner join emp_add e1 on e.empId=e1.empId

Output

 

Outer Join

 

There are three types of Outer Join

1. Left Outer Join
2. Right Outer Join
3. Full Outer Join

Left Outer Join

 

The result of the Left Outer Join contains all the records of the left table and if any record of the left table does not match the right table than it returns Null for the right side table.

select e.empId,e.empName,e1.empAdd from emp e left outer join emp_add e1 on e.empId=e1.empId

Output

 

Right Outer Join

 

The result of the Right Outer Join contains all the records of the right table and if any record of the right table does not match the Left table than it returns Null for the left side table.

select e.empId,e.empName,e1.empAdd from emp e right outer join emp_add e1 on e.empId=e1.empId

Output

 

 

Full Outer Join

 

A Full Outer Join fetches all records of both tables; where the record does not match, it returns Null.

select e.empId,e.empName,e1.empAdd from emp e full outer join emp_add e1 on e.empId=e1.empId

Output

 

 

Cross Join

 

This join is a Cartesian join. The result of a Cross Join contains records that are the multiplication of the records from both tables. 

select e.empId,e.empName,e1.empAdd from emp e cross join emp_add e1

Output

 

 

Here I create a table to explain self join

create table emp_mngr(empName varchar(15),mngrName varchar(15))

Insertion of data

insert into emp_mngr
select 'ravi','Gaurav'union all
select'Gaurav','tom'union all
select 'sem','singh'union all
select 'singh','arora

Output  

select * from emp_mngr

 

Self Join

 

In the Self Join a table is joined to itself. A Self Join can be an Inner Join or Outer Join. In the given example we find the employees that are the manager of other employees.

select e.empName,e.mngrName from emp_mngr e inner join emp_mngr e1 on e.empName=e1.mngrName

Output

 

 

Summary

 

In this article, I described joins in SQL Server. I hope this article has helped you in understanding this topic. Please share it. If you know more about this, your feedback and constructive contributions are welcome.