MySQL supports transaction processing, and uses the InnoDB storage engine to ensure data consistency and integrity. 1. Transactions are a set of SQL operations, either all succeed or all fail to roll back; 2. ACID attributes include atomicity, consistency, isolation and persistence; 3. The statements that manually control transactions are STARTTRANSACTION, COMMIT and ROLLBACK; 4. The four isolation levels include read not committed, read submitted, repeatable read and serialization; 5. Use transactions correctly to avoid long-term operation, turn off automatic commits, and reasonably handle locks and exceptions. Through these mechanisms, MySQL can achieve high reliability and concurrent control.

Character set and sorting rules issues are common when cross-platform migration or multi-person development, resulting in garbled code or inconsistent query. There are three core solutions: First, check and unify the character set of database, table, and fields to utf8mb4, view through SHOWCREATEDATABASE/TABLE, and modify it with ALTER statement; second, specify the utf8mb4 character set when the client connects, and set it in connection parameters or execute SETNAMES; third, select the sorting rules reasonably, and recommend using utf8mb4_unicode_ci to ensure the accuracy of comparison and sorting, and specify or modify it through ALTER when building the library and table.

iPhone does not support creating contact groups directly in the address book application, but similar functions can be achieved through the following methods: 1. Use the "Group" function in the address book application, click "Edit" > "Add Group" to create a custom group; 2. Add each contact to the corresponding group by editing it; 3. If you need to send a group message, you can create a new multi-person conversation in the information application; 4. Use iCloud or Gmail to synchronize tagged groups to facilitate the management of a large number of contacts on the computer. These methods are used in conjunction with efficient management of contact groups.

To design a reliable MySQL backup solution, 1. First, clarify RTO and RPO indicators, and determine the backup frequency and method based on the acceptable downtime and data loss range of the business; 2. Adopt a hybrid backup strategy, combining logical backup (such as mysqldump), physical backup (such as PerconaXtraBackup) and binary log (binlog), to achieve rapid recovery and minimum data loss; 3. Test the recovery process regularly to ensure the effectiveness of the backup and be familiar with the recovery operations; 4. Pay attention to storage security, including off-site storage, encryption protection, version retention policy and backup task monitoring.

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

A trigger is an automatically executed database object in MySQL that is used to perform predefined SQL operations when a specific event occurs. It can automatically update timestamps, verify or record data changes, maintain redundant fields, implement cascading operations, etc. To create a trigger, you need to specify the trigger timing (BEFORE/AFTER), event type (INSERT/UPDATE/DELETE) and execution logic, such as automatically populating the created_at field with BEFOREINSERT. When using it, you should pay attention to problems such as debugging difficulties, performance impact, high maintenance costs and inapplicability to distributed systems. It is recommended to keep the logic simple and make comments. Common scenarios include recording modification logs, restricting illegal operations, synchronous update of statistics tables and automatic filling

The MySQL query optimizer selects the optimal execution plan based on statistical information. The core mechanism is a cost-based model (CBO), which estimates I/O and CPU costs to determine the execution path; 1. Perform ANALYZETABLE regularly to ensure the accuracy of statistical information; 2. Indexes are not always used, such as querying large amounts of data or function operations may fail; 3. It is recommended to use EXPLAIN to view the execution plan, create overlay indexes, and avoid implicit type conversion; 4. The optimizer can be booted through USEINDEX or FORCEINDEX, but be cautious; 5. Rewriting the SQL structure and controlling the connection order can also affect the optimization results. Mastering these logic and combining tool analysis can help to optimize efficiently.