UNION vs. UNION ALL: When Should You Use Each?

CTEs are a feature introduced by MySQL8.0 to improve the readability and maintenance of complex queries. 1. CTE is a temporary result set, which is only valid in the current query, has a clear structure, and supports duplicate references; 2. Compared with subqueries, CTE is more readable, reusable and supports recursion; 3. Recursive CTE can process hierarchical data, such as organizational structure, which needs to include initial query and recursion parts; 4. Use suggestions include avoiding abuse, naming specifications, paying attention to performance and debugging methods.

MySQL query performance optimization needs to start from the core points, including rational use of indexes, optimization of SQL statements, table structure design and partitioning strategies, and utilization of cache and monitoring tools. 1. Use indexes reasonably: Create indexes on commonly used query fields, avoid full table scanning, pay attention to the combined index order, do not add indexes in low selective fields, and avoid redundant indexes. 2. Optimize SQL queries: Avoid SELECT*, do not use functions in WHERE, reduce subquery nesting, and optimize paging query methods. 3. Table structure design and partitioning: select paradigm or anti-paradigm according to read and write scenarios, select appropriate field types, clean data regularly, and consider horizontal tables to divide tables or partition by time. 4. Utilize cache and monitoring: Use Redis cache to reduce database pressure and enable slow query

TooptimizecomplexJOINoperationsinMySQL,followfourkeysteps:1)EnsureproperindexingonbothsidesofJOINcolumns,especiallyusingcompositeindexesformulti-columnjoinsandavoidinglargeVARCHARindexes;2)ReducedataearlybyfilteringwithWHEREclausesandlimitingselected

MySQL's EXPLAIN is a tool used to analyze query execution plans. You can view the execution process by adding EXPLAIN before the SELECT query. 1. The main fields include id, select_type, table, type, key, Extra, etc.; 2. Efficient query needs to pay attention to type (such as const, eq_ref is the best), key (whether to use the appropriate index) and Extra (avoid Usingfilesort and Usingtemporary); 3. Common optimization suggestions: avoid using functions or blurring the leading wildcards for fields, ensure the consistent field types, reasonably set the connection field index, optimize sorting and grouping operations to improve performance and reduce capital

There are three ways to connect Excel to MySQL database: 1. Use PowerQuery: After installing the MySQLODBC driver, establish connections and import data through Excel's built-in PowerQuery function, and support timed refresh; 2. Use MySQLforExcel plug-in: The official plug-in provides a friendly interface, supports two-way synchronization and table import back to MySQL, and pay attention to version compatibility; 3. Use VBA ADO programming: suitable for advanced users, and achieve flexible connections and queries by writing macro code. Choose the appropriate method according to your needs and technical level. PowerQuery or MySQLforExcel is recommended for daily use, and VBA is better for automated processing.

The security of remote access to MySQL can be guaranteed by restricting permissions, encrypting communications, and regular audits. 1. Set a strong password and enable SSL encryption. Force-ssl-mode=REQUIRED when connecting to the client; 2. Restrict access to IP and user rights, create a dedicated account and grant the minimum necessary permissions, and disable root remote login; 3. Configure firewall rules, close unnecessary ports, and use springboard machines or SSH tunnels to enhance access control; 4. Enable logging and regularly audit connection behavior, use monitoring tools to detect abnormal activities in a timely manner to ensure database security.

CTE is a temporary result set in MySQL used to simplify complex queries. It can be referenced multiple times in the current query, improving code readability and maintenance. For example, when looking for the latest orders for each user in the orders table, you can first obtain the latest order date for each user through the CTE, and then associate it with the original table to obtain the complete record. Compared with subqueries, the CTE structure is clearer and the logic is easier to debug. Usage tips include explicit alias, concatenating multiple CTEs, and processing tree data with recursive CTEs. Mastering CTE can make SQL more elegant and efficient.

Why do I need SSL/TLS encryption MySQL connection? Because unencrypted connections may cause sensitive data to be intercepted, enabling SSL/TLS can prevent man-in-the-middle attacks and meet compliance requirements; 2. How to configure SSL/TLS for MySQL? You need to generate a certificate and a private key, modify the configuration file to specify the ssl-ca, ssl-cert and ssl-key paths and restart the service; 3. How to force SSL when the client connects? Implemented by specifying REQUIRESSL or REQUIREX509 when creating a user; 4. Details that are easily overlooked in SSL configuration include certificate path permissions, certificate expiration issues, and client configuration requirements.