The computer is stuck in the "Undo Changes made to the computer" interface, which is a common problem after the Windows update fails. It is usually caused by the stuck rollback process and cannot enter the system normally. 1. First of all, you should wait patiently for a long enough time, especially after restarting, it may take more than 30 minutes to complete the rollback, and observe the hard disk light to determine whether it is still running. 2. If there is no progress for a long time, you can force shut down and enter the recovery environment (WinRE) multiple times, and try to start repair or system restore. 3. After entering safe mode, you can uninstall the most recent update records through the control panel. 4. Use the command prompt to execute the bootrec command in the recovery environment to repair the boot file, or run sfc/scannow to check the system file. 5. The last method is to use the "Reset this computer" function

When handling NULL values ??in MySQL, please note: 1. When designing the table, the key fields are set to NOTNULL, and optional fields are allowed NULL; 2. ISNULL or ISNOTNULL must be used with = or !=; 3. IFNULL or COALESCE functions can be used to replace the display default values; 4. Be cautious when using NULL values ??directly when inserting or updating, and pay attention to the data source and ORM framework processing methods. NULL represents an unknown value and does not equal any value, including itself. Therefore, be careful when querying, counting, and connecting tables to avoid missing data or logical errors. Rational use of functions and constraints can effectively reduce interference caused by NULL.

When encountering the "RPCserverisunavailable" problem, first confirm whether it is a local service exception or a network configuration problem. 1. Check and start the RPC service to ensure that its startup type is automatic. If it cannot be started, check the event log; 2. Check the network connection and firewall settings, test the firewall to turn off the firewall, check DNS resolution and network connectivity; 3. Run the sfc/scannow and DISM commands to repair the system files; 4. Check the group policy and domain controller status in the domain environment, and contact the IT department to assist in the processing. Gradually check it in sequence to locate and solve the problem.

Turn on MySQL slow query logs and analyze locationable performance issues. 1. Edit the configuration file or dynamically set slow_query_log and long_query_time; 2. The log contains key fields such as Query_time, Lock_time, Rows_examined to assist in judging efficiency bottlenecks; 3. Use mysqldumpslow or pt-query-digest tools to efficiently analyze logs; 4. Optimization suggestions include adding indexes, avoiding SELECT*, splitting complex queries, etc. For example, adding an index to user_id can significantly reduce the number of scanned rows and improve query efficiency.

mysqldump is a common tool for performing logical backups of MySQL databases. It generates SQL files containing CREATE and INSERT statements to rebuild the database. 1. It does not back up the original file, but converts the database structure and content into portable SQL commands; 2. It is suitable for small databases or selective recovery, and is not suitable for fast recovery of TB-level data; 3. Common options include --single-transaction, --databases, --all-databases, --routines, etc.; 4. Use mysql command to import during recovery, and can turn off foreign key checks to improve speed; 5. It is recommended to test backup regularly, use compression, and automatic adjustment.

The problem of slowing right-click menus is usually caused by extensions or third-party software loaded by the system. Solutions include troubleshooting plug-ins, optimizing settings, and uninstalling suspicious software. 1. Use the ShellExView tool to view and disable non-essential Shell extensions, and gradually test to find plug-ins that slow down the right-click menu; 2. For advanced users, you can lower the menu delay time to 0 or 200 milliseconds by modifying the MenuShowDelay key value in the registry to speed up the response speed, but you need to be careful to backup before operation to avoid causing system abnormalities; 3. Uninstall or update software that may cause conflicts such as old compression tools, screenshot software, antivirus software, etc., and observe whether the right-click menu returns to normal. If the problem is alleviated, it means that it is the performance problem caused by the software.

MySQL paging is commonly implemented using LIMIT and OFFSET, but its performance is poor under large data volume. 1. LIMIT controls the number of each page, OFFSET controls the starting position, and the syntax is LIMITNOFFSETM; 2. Performance problems are caused by excessive records and discarding OFFSET scans, resulting in low efficiency; 3. Optimization suggestions include using cursor paging, index acceleration, and lazy loading; 4. Cursor paging locates the starting point of the next page through the unique value of the last record of the previous page, avoiding OFFSET, which is suitable for "next page" operation, and is not suitable for random jumps.

GROUPBY is used to group data by field and perform aggregation operations, and HAVING is used to filter the results after grouping. For example, using GROUPBYcustomer_id can calculate the total consumption amount of each customer; using HAVING can filter out customers with a total consumption of more than 1,000. The non-aggregated fields after SELECT must appear in GROUPBY, and HAVING can be conditionally filtered using an alias or original expressions. Common techniques include counting the number of each group, grouping multiple fields, and filtering with multiple conditions.