MySQL UPDATE JOIN

The UPDATE JOIN statement in MySQL provides a way to update one table based on the information from another table. This is especially useful when you need to update many rows or when the rows you want to update are in some way related to the contents of another table.

Syntax 

The syntax for the UPDATE JOIN statement in MySQL is as follows:

UPDATE table1
JOIN table2
ON table1.column1 = table2.column2
SET table1.columnToUpdate = table2.columnToCopyFrom
WHERE conditions;

In this syntax, table1 is the table to be updated, table2 is the table providing new data, and the ON clause specifies how the two tables should be joined. The SET clause specifies which column(s) to update and where to get the new data.

Demo Database 

Let's consider two related tables, Orders and Customers, for our examples: 

Orders

OrderID	Product	CustomerID
1	Apples	123
2	Bananas	456
3	Grapes	789

Customers

CustomerID	Name
123	John Doe
456	Jane Smith
789	Mary Johnson

Examples 

UPDATE JOIN 

Suppose we want to add a new CustomerName column in the Orders table and populate it with data from the Customers table:

ALTER TABLE Orders ADD COLUMN CustomerName VARCHAR(255);

UPDATE Orders
JOIN Customers ON Orders.CustomerID = Customers.CustomerID
SET Orders.CustomerName = Customers.Name;

This statement first adds a new column CustomerName to the Orders table. The UPDATE JOIN statement then fills this new column with the names of customers from the Customers table where the CustomerID matches.

Summary 

The UPDATE JOIN statement in MySQL is a powerful tool when you need to update one table based on the data in another. It enables you to maintain consistency across tables and perform complex updates without needing to manually adjust each row.