When Left Join gives result like Right Join?

SQL >   SQL Joins >   Left Join  

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Answer:

Left Table

SubjectId	SubjectName
1	C Language
2	Java Language

Right Table

ChapterId	ChapterName	SubjectId
1	Introduction C	1
2	Operator Java	2
3	Operator python	3
4	Operator R	3

For both of the cases Result will be like this

SubjectId	SubjectName	ChapterId	ChapterName
1	C Language	1	Introduction C
2	Java Language	2	Operator Java
NULL	NULL	3	Operator python
NULL	NULL	4	Operator R

Example: Right Join

Code:

SELECT s.SubjectId as SubjectId, s.SubjectName as SubjectName,
 c.ChapterId as ChapterId, c.ChapterName as ChapterName
FROM Subjects as s 
RIGHT JOIN Chapters as c
ON s.SubjectId = c.SubjectId

Example: Left Join which will give output same as Right Join.

We can say this is as a mirror effect.

Code:

SELECT s.SubjectId as SubjectId, s.SubjectName as SubjectName,
 c.ChapterId as ChapterId, c.ChapterName as ChapterName
FROM Chapters as c 
LEFT JOIN Subjects as s 
ON s.SubjectId = c.SubjectId

Example: Left Join will give below result without mirror effect.

Code:

SELECT s.SubjectId as SubjectId, s.SubjectName as SubjectName,
 c.ChapterId as ChapterId, c.ChapterName as ChapterName
FROM Subjects as s
LEFT JOIN Chapters as c
ON s.SubjectId = c.SubjectId

SubjectId	SubjectName	ChapterId	ChapterName
1	C Language	1	Introduction C
2	Java Language	2	Operator Java

Prerequisite Codes

If you don't have the above tables create those table from the below code and let's practice.

Code:

USE SQLExamples

DROP TABLE Subjects
DROP TABLE Chapters

CREATE TABLE Subjects(
	SubjectId INT,	
	SubjectName VARCHAR(30)
)

SELECT * FROM Subjects

CREATE TABLE Chapters(
	ChapterId INT,	
	ChapterName VARCHAR(30),
	SubjectId int,
)

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