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SQL Server Joins

13 Aug 2022

SQL JOIN

The statement JOIN is used to combine the rows of two or more tables based  on a common column.

The different types of JOIN statement used in SQL are

  • INNER JOIN or JOIN – combines the data that matches  in both tables.
  • LEFT JOIN or LEFT OUTER JOIN – combines all the datas of left table with the datas from right table that matches.
  • RIGHT JOIN or RIGHT OUTER JOIN – combines all the datas of right table with the datas from left table that matches.
  • FULL JOIN or FULL OUTER JOIN – combines all the datas either from left or right table whenever there is a match found.

Let us consider an example:

Create a database with a name “StudentResults”

create database  StudentResults

Create a table “studentdetails” with following snippet

CREATE TABLE studentdetails (

regno int,

LastName varchar(255),

FirstName varchar(255),

age int,

dummyno int

);

Let us consider the following datas in table “studentdetails”

Create another table “result” with the snippet

CREATE TABLE result (

dummyno int,

marks int,

result varchar(10)

);

Let us consider the following datas in table “result”

 

INNER JOIN:

Inner Join is the most simplest Join. When inner join keyword is used in two tables, it will create a resulting table with combining the rows of both the tables until the condition is satisfied

For the above considered example, when inner join statement is used as follows

SELECT studentdetails.regno, studentdetails.FirstName, studentdetails.LastName, studentdetails.age, result.marks, result.result

FROM result

INNER JOIN studentdetails

ON studentdetails.dummyno=result.dummyno;

The resulting table will be

LEFT JOIN:

 Left join is also called as Left outer join. When left join keyword is used in two tables, it will create a resulting table with combining all the datas of left table with the datas from right table that matches.

For the considered example, when left join statement is used as follows

SELECT studentdetails.regno, studentdetails.FirstName, studentdetails.LastName, studentdetails.age, result.marks, result.result

FROM studentdetails

LEFT JOIN result

ON studentdetails.dummyno=result.dummyno

ORDER BY studentdetails.regno;

The resulting table will be

RIGHT JOIN:

 Right join is also called as right outer join. When right join keyword is used in two tables, it will create a resulting table with combining all the datas of right table with the datas from left table that matches.

For the considered example, when right join statement is used as follows

SELECT studentdetails.regno, studentdetails.FirstName, studentdetails.LastName, studentdetails.age, result.marks, result.result

FROM studentdetails

RIGHT JOIN result

ON studentdetails.dummyno=result.dummyno

ORDER BY studentdetails.regno;

The resulting table will be

FULL JOIN:

 Full join is also called as Outer join. When full join keyword is used in two tables, it will create a resulting table with combining all the datas either from left or right table whenever there is a match found.

For the considered example, when full join statement is used as follows

SELECT studentdetails.regno, studentdetails.FirstName, studentdetails.LastName, studentdetails.age, result.marks, result.result

FROM studentdetails

FULL OUTER JOIN result

ON studentdetails.dummyno=result.dummyno

ORDER BY studentdetails.regno;

The resulting table will be

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