In MySQL, add fields using ALTERTABLEtable_nameADDCOLUMNnew_columnVARCHAR(255)AFTERexisting_column, delete fields using ALTERTABLEtable_nameDROPCOLUMNcolumn_to_drop. When adding fields, you need to specify a location to optimize query performance and data structure; before deleting fields, you need to confirm that the operation is irreversible; modifying table structure using online DDL, backup data, test environment, and low-load time periods is performance optimization and best practice.

Starting the rollback function on Windows 11 must be performed within 10 days after the upgrade. The steps are as follows: 1. Open "Settings", 2. Enter "System", 3. Find the "Recover" option, 4. Start rollback, 5. Confirm the rollback. After rollback, you need to pay attention to data backup, software compatibility and driver updates.

C drive can expand capacity in five ways: 1. Use Windows disk management tools to expand the volume, but there must be unallocated space; 2. Use third-party software such as EaseUS or AOMEI to adjust the partition size; 3. Use Diskpart command line tools to expand the C drive, suitable for users who are familiar with the command line; 4. Repartition and format the hard disk, but it will cause data loss and data needs to be backed up; 5. Use external storage devices as C drive expansion, transfer folders through symbolic links or modification of the registry.

MySQL is an open source relational database management system, mainly used to store, organize and retrieve data. Its main application scenarios include: 1. Web applications, such as blog systems, CMS and e-commerce platforms; 2. Data analysis and report generation; 3. Enterprise-level applications, such as CRM and ERP systems; 4. Embedded systems and Internet of Things devices.

To develop a complete Python Web application, follow these steps: 1. Choose the appropriate framework, such as Django or Flask. 2. Integrate databases and use ORMs such as SQLAlchemy. 3. Design the front-end and use Vue or React. 4. Perform the test, use pytest or unittest. 5. Deploy applications, use Docker and platforms such as Heroku or AWS. Through these steps, powerful and efficient web applications can be built.

Avoiding SQL injection in PHP can be done by: 1. Use parameterized queries (PreparedStatements), as shown in the PDO example. 2. Use ORM libraries, such as Doctrine or Eloquent, to automatically handle SQL injection. 3. Verify and filter user input to prevent other attack types.

Create a SQLite database in Python using the sqlite3 module. The steps are as follows: 1. Connect to the database, 2. Create a cursor object, 3. Create a table, 4. Submit a transaction, 5. Close the connection. This is not only simple and easy to do, but also includes optimizations and considerations such as using indexes and batch operations to improve performance.

Java middleware is a software that connects operating systems and application software, providing general services to help developers focus on business logic. Typical applications include: 1. Web server (such as Tomcat and Jetty), which handles HTTP requests; 2. Message queue (such as Kafka and RabbitMQ), which handles asynchronous communication; 3. Transaction management (such as SpringTransaction), which ensures data consistency; 4. ORM framework (such as Hibernate and MyBatis), which simplifies database operations.