Cross Join vs Inner Join in Sql

Question

What is the difference between CROSS JOIN and INNER JOIN?

CROSS JOIN:

SELECT 
    Movies.CustomerID, Movies.Movie, Customers.Age, 
    Customers.Gender, Customers.[Education Level], 
    Customers.[Internet Connection], Customers.[Marital Status], 
FROM   
    Customers 
CROSS JOIN 
    Movies

INNER JOIN:

SELECT 
    Movies.CustomerID, Movies.Movie, Customers.Age, 
    Customers.Gender, Customers.[Education Level], 
    Customers.[Internet Connection], Customers.[Marital Status]
FROM   
    Customers 
INNER JOIN 
    Movies ON Customers.CustomerID = Movies.CustomerID

Which one is better and why would I use either one?

Accepted Answer

Here is the best example of Cross Join and Inner Join.

Consider the following tables

TABLE : Teacher

x------------------------x
| TchrId   | TeacherName | 
x----------|-------------x
|    T1    |    Mary     |
|    T2    |    Jim      |
x------------------------x

TABLE : Student

x--------------------------------------x
|  StudId  |    TchrId   | StudentName | 
x----------|-------------|-------------x            
|    S1    |     T1      |    Vineeth  |
|    S2    |     T1      |    Unni     |
x--------------------------------------x

Must Read

1. INNER JOIN

Inner join selects the rows that satisfies both the table.

Consider we need to find the teachers who are class teachers and their corresponding students. In that condition, we need to apply JOIN or INNER JOIN and will

Query

SELECT T.TchrId,T.TeacherName,S.StudentName 
FROM #Teacher T
INNER JOIN #Student S ON T.TchrId = S.TchrId

SQL FIDDLE

Result

x--------------------------------------x
|  TchrId  | TeacherName | StudentName | 
x----------|-------------|-------------x            
|    T1    |     Mary    |    Vineeth  |
|    T1    |     Mary    |    Unni     |
x--------------------------------------x

Cross Join vs Inner Join in Sql

11 Answers

Must Read

1. INNER JOIN

Marcus Vance