MySQL: No Database Selected - Select the Default DB
Introduction
In MySQL, when a connection is established with the server, it is essential to select a database before executing any queries. If a database is not selected, the error message "No database selected" will be thrown. This article will explain why this error occurs and how to select a default database in MySQL.
Error Message: No database selected
The error "No database selected" occurs when a query is executed without specifying a database. Consider the following example:
SELECT * FROM customers;
This query will result in the error message "No database selected" because there is no database specified to perform the query.
Selecting the Default Database
To avoid the "No database selected" error, you need to select a default database. A default database is a database that is automatically used for queries if no database is specified explicitly.
To select the default database, you can use the USE
statement followed by the database name. Here's an example:
USE mydatabase;
In the above example, the database named "mydatabase" is selected as the default database. Once the default database is set, you can execute queries without explicitly specifying the database.
Example Usage
Let's consider a scenario where we have a database named "mydatabase" containing a table called "employees." To select the default database and retrieve all employees' information, you can follow these steps:
- Establish a connection to the MySQL server.
- Select the default database using the
USE
statement.
USE mydatabase;
- Execute the query to retrieve all employees' information.
SELECT * FROM employees;
Flowchart
The following is a flowchart representing the process of selecting the default database in MySQL:
flowchart TD
A[Establish Connection]
B[Select Default Database]
C[Execute Queries]
A --> B
B --> C
Conclusion
In MySQL, it is essential to select a database before executing any queries. If a database is not selected, the error message "No database selected" will be thrown. To avoid this error, you can use the USE
statement to select a default database. Once the default database is set, you can execute queries without explicitly specifying the database. Following the steps mentioned in this article, you can easily select a default database and perform queries seamlessly.