How to completely delete data from a MySQL database

How to completely delete data in MySQL requires specific code examples

Overview:
MySQL is a commonly used relational database management system, and deleting data is a database operation One of the most common requirements. But a simple DELETE statement only marks the data for deletion, rather than truly deleting it completely. This article will introduce how to use MySQL to completely delete data and provide specific code examples.

Method 1: Use DELETE statement

1. Execute DELETE statement
   DELETE FROM table_name WHERE condition;
   This is a common syntax for deleting data. Among them, table_name is the name of the table where data is to be deleted, and condition is the condition for deletion, which can be set according to specific needs.
2. View deletion results
   SELECT * FROM table_name;
   Execute the above query statement. If the deletion is successful, the relevant data will no longer be displayed.

Although you can see that the data is not displayed using the DELETE statement, the data is actually not completely deleted. This is because MySQL has transactional features, and modern MySQL versions have transactions enabled by default. In a transaction, when the DELETE statement is executed, the database actually marks the data as deleted, but the data is not actually physically deleted.

Method 2: Use the TRUNCATE statement

1. Execute the TRUNCATE statement
   TRUNCATE TABLE table_name;
   Use the TRUNCATE statement to completely delete the data and clear all the data in the table. After the TRUNCATE statement is executed, the structure of the table will be retained.
2. View deletion results
   SELECT * FROM table_name;
   When you execute the above query statement, no data will be displayed.

Compared with the DELETE statement, the TRUNCATE statement is more effective for completely deleting data. It will delete the data from the physical level and is very suitable for scenarios where you need to manually clear the data in the table. However, the TRUNCATE statement cannot delete data under specific conditions, but can only delete data in the entire table.

Method 3: Use the DROP statement

1. Execute the DROP statement
   DROP TABLE table_name;
   The DROP statement can completely delete the entire table, including the table structure and data.
2. View deletion results
   SELECT * FROM table_name;
   Executing the above query statement will prompt an error that the table does not exist.

You need to be careful when using the DROP statement, because it will not only delete data, but also delete the entire table and its structure. Before using the DROP statement, be sure to back up important data.

To sum up, the effect of deleting data can be achieved by using DELETE statement, TRUNCATE statement and DROP statement. Choose the appropriate method based on your specific needs. A specific example is given below:

Example: Use the DELETE statement to delete data under specific conditions

DELETE FROM employees WHERE age > 30;
In this example, employees are deleted Data for employees older than 30 in the table.

Summary:
Deleting data is a common requirement in database operations. MySQL provides a variety of methods to achieve the effect of completely deleting data. The effect of deleting data can be achieved using the DELETE statement, TRUNCATE statement and DROP statement. Choose the appropriate method based on specific needs and back up important data before operation.

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