8+ Join 使い方 Article

Introduction

Join is an important command in the world of technology. If you are new to this term, then you have come to the right place. Join is a command that allows you to join two or more tables in a database. This command is used to combine data from multiple tables into a single result set. In this article, we will discuss the best ways to use Join in 2023.

What is Join?

Join is a command that is used to combine data from two or more tables based on a common column between them. The common column acts as a join condition. There are four types of joins: inner join, left join, right join, and full outer join. The type of join that you use depends on the data that you want to retrieve from the tables.

Inner Join

Inner join is a type of join that returns only the matching rows from both tables. The join condition is specified using the ON keyword. This type of join is useful when you want to retrieve only the data that is present in both tables.

Example:

SELECT * FROM table1 INNER JOIN table2 ON table1.column1 = table2.column2;

Left Join

Left join is a type of join that returns all the rows from the left table and the matching rows from the right table. If there is no matching row in the right table, then the result will contain NULL values. This type of join is useful when you want to retrieve all the data from the left table and the matching data from the right table.

Example:

SELECT * FROM table1 LEFT JOIN table2 ON table1.column1 = table2.column2;

Right Join

Right join is a type of join that returns all the rows from the right table and the matching rows from the left table. If there is no matching row in the left table, then the result will contain NULL values. This type of join is useful when you want to retrieve all the data from the right table and the matching data from the left table.

Example:

SELECT * FROM table1 RIGHT JOIN table2 ON table1.column1 = table2.column2;

Full Outer Join

Full outer join is a type of join that returns all the rows from both tables. If there is no matching row in either table, then the result will contain NULL values. This type of join is useful when you want to retrieve all the data from both tables.

Example:

SELECT * FROM table1 FULL OUTER JOIN table2 ON table1.column1 = table2.column2;

Conclusion

Join is a powerful command that is used to combine data from multiple tables. In this article, we have discussed the four types of joins: inner join, left join, right join, and full outer join. Each type of join is used for a specific purpose. By understanding the differences between these types of joins, you can choose the right one for your specific needs.