INNER JOIN vs. OUTER JOIN: What's the Difference and When Should I Use Each?

Database connection: comparison of Inner Join and Out Join

In the database operation, the connection operation is the key to combining multiple table data. Inner join and Outjoin are two types of connection types. This article will explore their key differences and practical applications.

Inner Join: intersection

Inner Join selects two or more columns in different tables. In conceptual point of view, it obtains the intersection of two collection and is expressed in the overlapping part of Ventu. Only in the two tables at the same time will include in the output.

OUTER JOIN: Collection

Unlike Inner Join, OUTER JOIN contains all the rows in the specified table, regardless of whether they have matching in other tables. This operation effectively creates a parallelism that is represented by the combination area of ​​Ventu. Outjoin type

Outjoin is divided into three types:

left outer join:

Get all the lines on the left and any matching rows in the right table. The row without matching in the left table on the right table will contain the NULL value.

Right Outr Join:

Similar to LEFT OUTER JOIN, but get all lines on the right table and the lines matched in the left table.
• Full Outr Join: All lines of the two tables are combined, and the matching items of missing missing are filled with NULL values.
• Actual examples
• Considering the following tables containing customers and their order data: Customer (ID, name)
Orders (ID, CUSTOMER_ID, Product)

Inner Join:

This query will return only customers who have placed orders.

left outer join:

This query will return to all customers, including customers without orders, the order information will be NULL.

Right Outr Join:

SELECT *
FROM customer
INNER JOIN orders ON customer.id = orders.customer_id;

This query will return all orders, including orders placed by customers in the Customer table, and customer information will be NULL. Full Outr Join:

SELECT *
FROM customer
LEFT OUTER JOIN orders ON customer.id = orders.customer_id;

This query will return all customers and all orders to fill in the lack of matching items with NULL values.

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