How to perform cross-database queries in MySQL?

There are two methods for performing cross-database queries in MySQL.

1. Utilize fully qualified table names: Add the database name as a prefix to the table name in the query statement, for example:

SELECT db1.table1.column1, db2.table2.column2 
FROM db1.table1 
JOIN db2.table2 ON db1.table1.id = db2.table2.id;

1. You can switch to the database you want to query first using the USE statement, and then directly query the table. For example:

USE db1;
SELECT column1 FROM table1;
USE db2;
SELECT column2 FROM table2;

Cross-database queries can be achieved using any method. However, it is important to note that such queries may impact performance, so it is advised to minimize them when designing databases.