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  • mysql flush privileges what it does
    mysql flush privileges what it does
    FLUSHPRIVILEGES is used to reload MySQL's permission table so that manual modified permissions take effect immediately. 1. When directly modifying system tables such as mysql.user or mysql.db, you must execute this command to load the changes from disk to memory; 2. When using standard permission management statements such as GRANT, REVOKE, CREATEUSER, etc., you do not need to execute this command because the permissions have been automatically refreshed; 3. This command will not restart the service, repair configuration errors, or disconnect the current connection, and only notify MySQL to reread the authorization table content.
    Mysql Tutorial . Database 447 2025-07-13 01:27:31
  • mysql auto_increment reset
    mysql auto_increment reset
    To reset the starting value of the MySQL self-increment field, you can set the AUTO_INCREMENT value through ALTERTABLE, clear the table and reset it with TRUNCATE, or manually set it after DELETE; you can check the current self-increment value and execute SHOWCREATETABLEyour_table_name; information similar to AUTO_INCREMENT=100 will be displayed in the output; when setting manually, make sure that the setting value is the current maximum ID 1, otherwise MySQL will automatically adjust; TRUNCATE will delete data and reset the self-increment value, but DELETE will not; be careful that the actual maximum ID 1 may be restored after the InnoDB engine restarts to avoid conflicts caused by too small settings.
    Mysql Tutorial . Database 182 2025-07-13 00:56:00
  • mysql recursive cte example
    mysql recursive cte example
    MySQL's RecursiveCTE is mainly used to process hierarchical data. 1. It realizes traversal of the tree structure through initial queries and recursive queries, such as finding all subordinates of a certain employee; 2. It can be used to generate numerical sequences, such as 1 to 100; 3. When using them, you need to pay attention to avoid infinite loops, control recursive depth, optimize indexes, and first test small data to verify the correctness of the logic.
    Mysql Tutorial . Database 1039 2025-07-12 02:28:40
  • Best Practices for Securing Remote Access to MySQL
    Best Practices for Securing Remote Access to MySQL
    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.
    Mysql Tutorial . Database 474 2025-07-12 02:25:11
  • mysql find duplicate records in a table
    mysql find duplicate records in a table
    Repetition checking can be implemented in MySQL through GROUPBY and HAVING; single-field repeated use of SELECT field COUNT and grouped, such as SELECTemail, COUNT(*)FROMtableGROUPBYemailHAVINGCOUNT>1; multiple fields need to be grouped at the same time, such as SELECTname, birthdayFROMtableGROUPBYname, birthdayHAVINGCOUNT>1; if specific records are required, you can combine JOIN query; performance optimization includes adding composite indexes, limiting query scope and using LIMIT to reduce data scans.
    Mysql Tutorial . Database 184 2025-07-12 02:23:50
  • Using Common Table Expressions (CTEs) in MySQL 8
    Using Common Table Expressions (CTEs) in MySQL 8
    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 Tutorial . Database 913 2025-07-12 02:23:11
  • what is mysql query cache
    what is mysql query cache
    MySQLQueryCache is a built-in caching mechanism used to cache query statements and their results to improve the performance of duplicate queries. 1. It avoids repeated execution of the same query by directly returning cached results; 2. The cache is based on a complete SQL statement, and statement differences or table data changes will cause cache failure; 3. MySQL8.0 has completely removed this function due to poor concurrency performance, low hit rate and high maintenance costs; 4. Alternative solutions include using Redis/Memcached, database middleware ProxySQL, page cache and other more flexible and efficient caching strategies.
    Mysql Tutorial . Database 167 2025-07-12 02:20:51
  • Applying Aggregate Functions and GROUP BY in MySQL
    Applying Aggregate Functions and GROUP BY in MySQL
    The aggregation function is used to perform calculations on a set of values ??and return a single value. Common ones include COUNT, SUM, AVG, MAX, and MIN; GROUPBY groups data by one or more columns and applies an aggregation function to each group. For example, GROUPBYuser_id is required to count the total order amount of each user; SELECTuser_id, SUM(amount)FROMordersGROUPBYuser_id; non-aggregated fields must appear in GROUPBY; multiple fields can be used for multi-condition grouping; HAVING is used instead of WHERE after grouping; application scenarios such as counting the number of classified products, maximum ordering users, monthly sales trends, etc. Mastering these can effectively solve the number
    Mysql Tutorial . Database 329 2025-07-12 02:19:01
  • Implementing foreign key constraints and cascade actions in MySQL
    Implementing foreign key constraints and cascade actions in MySQL
    ToimplementforeignkeysandcascadeactionsinMySQL,useInnoDBtables,definerelationshipswithproperconstraints,andspecifyONDELETEorONUPDATECASCADEbehavior.1)EnsurebothtablesusetheInnoDBengine;2)Createaforeignkeythatreferencesaprimaryoruniquekeyinanothertabl
    Mysql Tutorial . Database 222 2025-07-12 02:17:21
  • mysql error 1205 lock wait timeout exceeded
    mysql error 1205 lock wait timeout exceeded
    MySQL error 1205: The core reason for Lockwaittimeoutexceeded is that the time when a transaction waits for a lock exceeds the set threshold (default 50 seconds), which is often caused by fierce resource competition, excessive transaction execution or failure to commit, and excessive lock range due to no appropriate index. Troubleshooting methods include: 1. Use SHOWENGINEINNODBSTATUS\G and information_schema.innodb_trx to view active transactions and lock waiting conditions; 2. Use PROCESSLIST to locate stuck SQL; 3. Adjust the innodb_lock_wait_timeout parameter as a temporary mitigation measure; 4. Optimize SQL and transactions
    Mysql Tutorial . Database 431 2025-07-12 02:14:31
  • how to enable general query log in mysql
    how to enable general query log in mysql
    The general query log can be enabled through commands or configuration files. 1. Check the status with SHOWVARIABLESLIKE'general_log%'; check whether it is ON; 2. Temporarily enable SETGLOBALgeneral_log=ON; restart fails; 3. Permanently enable general_log=1 and specified log path in my.cnf and restart MySQL service; 4. Pay attention to performance impact, disk space occupation, risk of sensitive data leakage and log format optional file or table storage.
    Mysql Tutorial . Database 329 2025-07-12 02:09:50
  • Analyzing Query Execution with MySQL EXPLAIN
    Analyzing Query Execution with MySQL EXPLAIN
    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
    Mysql Tutorial . Database 1056 2025-07-12 02:07:21
  • what is a primary key in mysql
    what is a primary key in mysql
    AprimarykeyinMySQLisaconstraintthatuniquelyidentifieseachrowinatable.1.Itensuresdatauniquenessandnon-nullvalues,eitherinasinglecolumnoracombinationofcolumns.2.Everytableshouldhaveaprimarykeytoenforceentityintegrityandallowreliabledistinctionbetweenre
    Mysql Tutorial . Database 178 2025-07-12 02:06:31
  • mysql error 1215 cannot add foreign key constraint
    mysql error 1215 cannot add foreign key constraint
    MySQL error "Error1215:Cannotaddforeignkeyconstraint" is usually caused by the foreign key setting that does not meet the prerequisites. 1. Data type mismatch: The data type, length, and symbol attributes of the foreign key and the primary key field must be the same; 2. The engine is inconsistent: Only the InnoDB engine supports foreign keys, so make sure that the table uses InnoDB; 3. Different character sets or sorting rules: It is recommended to unify the character set and sorting rules; 4. The field is not indexed: the foreign key field should be explicitly indexed; 5. The table or field name is incorrectly spelled: it is necessary to check whether it exists and whether it is spelled correctly. During the investigation, the above reasons can be corrected one by one.
    Mysql Tutorial . Database 948 2025-07-12 01:59:22

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