How To Use Cross Join In MySQL

Introduction

In this article, we learn how to use a cross-join and when we use it. To learn this topic is mandatory to know the concepts of joins, then you easily relate cross join. The join procedure known as a cross joins in MySQL returns the Cartesian sum of two or more tables. Each row from the first table is combined with each row from the second table, and so on, creating a new table with every possible combination of rows from each table. We will go through the cross-join syntax in MySQL and how to utilize it to get data from many tables. In order to better grasp how cross-joins function, we will also go through a few examples with various scenarios.

What is Cross Join in MySQL?

In MySQL, cross-join is one of the important joins that we used when we want all records from the joined tables. It returns the cartesian product of those tables is joined, which returns all conceivable combinations of rows from two or more participating tables

When we use Cross join?

Cross Join is similar to the cross product in relational algebra, the cross product provides unnecessary columns, but cross joins only provide necessary columns or data. When we want data that lies in two or more tables, then we use a cross-join. This is very easy to understand and use it. You assume two tables in the database, 'm' and 'n', then the output is 'm*n'.

Syntax

SELECT * FROM TABLE_1 CROSS JOIN TABLE_2;

Example Cross Join in MySQL In this example, we apply cross join between two tables, Table1 and Table2.

Table1

Table2

There is two tables, table1 and table2. In table2, Teacherid act as the primary key, and In table1, Teacherid act as a foreign key. So the query is.

SELECT * From Table1 CROSS JOIN Table2;

Result

Explanation

In this example, we use two Tables, table1 and table2 in table1, stored student records, and table2 stores teachers' records. So we want the student's and teachers' details. We write a query of the cross join those are written in above the example. After executing this query, the result comes is the combination of both tables.

How to use the Where Clause in Cross Join?

We also use the where clause in cross joins something according to need we use where clause. Syntax

SELECT * FROM TABLE_1 CROSS JOIN TABLE_2 WHERE "YOUR CONDITION TYPE HERE";

Example- In this example, we use the previous table those we use above the article

Table1

Table2

Query

SELECT * FROM Table1 CROSS JOIN Table2 WHERE Table1.StudentRollNo =3;

Result

Explanation In this example, we use cross-join with  Where Clause, which means that when that query run and the condition matches, then it will show the result. In above the example, we wrote the condition in the where clause, So it matches the condition and then returns the result  

Conclusion 

In this article, we learn lots of things, such that how to use a cross join and where we use a cross join,  also, look at where clause in cross join with an example. This is very easy to use and implement it. This is one of the important topics in MySQL. We use this cross-join lots of times during working in a database. The name of the table to join with is used together with the CROSS JOIN keyword. The article demonstrates how to execute a cross-join using SQL queries using two tables as examples. The result is a Cartesian product of the two tables that contains all conceivable combinations of rows. In conclusion, the article gives a concise explanation of how to aggregate rows from various tables in MySQL using cross-join.

FAQs

Q. What is a cross-join in MySQL?

A. cross-join in MySQL returns the Cartesian product of two or more tables, which means it combines each row of one table with each row of another table, resulting in a new table with all possible combinations.

Q. When do we use a cross-join in MySQL?

A. We use a cross-join in MySQL when we want all records from the joined tables and when we need to obtain data that exists in two or more tables.

Q. What is the syntax of a cross-join in MySQL?

A. The syntax of a cross-join in MySQL is: SELECT * FROM TABLE_1 CROSS JOIN TABLE_2;

Q. Can we use the WHERE clause in a cross-join query in MySQL?

A. Yes, we can use the WHERE clause in a cross-join query in MySQL to filter the results based on specific conditions.

Q. 5 Is a cross-join the same as a Cartesian product in relational algebra?

A. Yes, a cross-join is similar to a Cartesian product in relational algebra, as it provides all possible combinations of rows from two or more tables.