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
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
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
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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