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  • What is the process for upgrading MySQL from version 5.7 to 8.0?
    What is the process for upgrading MySQL from version 5.7 to 8.0?
    UpgradingMySQLfrom5.7to8.0requiresseveralkeysteps:first,checkcompatibilitybyreviewingdeprecatedfeaturesliketheutf8characterset,verifyingpluginsandstorageengines,andensuringapplication-levelcompatibilitywithORMs;second,backupalldatabasesusingmysqldump
    Mysql Tutorial . Database 462 2025-06-19 00:46:30
  • How to troubleshoot 100% CPU usage by the MySQL server?
    How to troubleshoot 100% CPU usage by the MySQL server?
    Common reasons why MySQL consumes 100% of CPU include slow queries, missing indexes, temporary tables or excessive sorting, and configuration issues. 1. First use SHOWPROCESSLIST to check active connections and resource-consuming operations; 2. Enable and analyze slow query log location historical issues; 3. Check Created_tmp_tables and Sort_merge_passes to judge temporary tables and sorting; 4. Use EXPLAIN to analyze SQL execution plans and optimize full table scanning and file sorting; 5. Check other factors such as connection count, statistical information updates and timing tasks. The above steps can gradually narrow the scope of problems and optimize performance bottlenecks.
    Mysql Tutorial . Database 635 2025-06-19 00:45:51
  • How to create a new user and grant it only SELECT and INSERT on a specific table?
    How to create a new user and grant it only SELECT and INSERT on a specific table?
    To create a new user and grant only SELECT and INSERT permissions to a specific table, first create the user using the CREATEUSER statement in MySQL, then authorize it through the GRANT statement, and execute FLUSHPRIVILEGES refresh permissions; in PostgreSQL, also first create the user using CREATEUSER, and then grant the permissions through the GRANTSELECT and INSERTONTABLE statements. 1. Create user: MySQL syntax is CREATEUSER'new_user'@'host'IDENTIFIEDBY'password'; PostgreSQL is CREATEUSE
    Mysql Tutorial . Database 763 2025-06-19 00:45:10
  • What are the most common string functions in MySQL?
    What are the most common string functions in MySQL?
    The most commonly used string functions in MySQL include: 1. CONCAT() is used to concatenate strings, such as merging names or URLs; 2. SUBSTRING() extracts substrings by position and length, suitable for obtaining file extensions, etc.; 3. UPPER() and LOWER() are case-based to standardize comparison or output; 4. TRIM(), LTRIM() and RTRIM() remove spaces to clean up user input data. These functions can efficiently handle the formatting, splicing and cleaning tasks of text data.
    Mysql Tutorial . Database 528 2025-06-19 00:43:01
  • Where is the MySQL configuration file my.cnf (or my.ini) located?
    Where is the MySQL configuration file my.cnf (or my.ini) located?
    MySQL configuration files are usually located in standard paths, such as Linux in /etc/my.cnf or /etc/mysql/my.cnf, macOS (Homebrew) in /usr/local/etc/my.cnf, Windows in the installation directory or Windows directory. You can confirm the specific path by command mysql--help|grep"Defaultoptions" or in MySQL shell; if it is not found, you can manually create and set basic content, pay attention to permission issues and rings.
    Mysql Tutorial . Database 237 2025-06-19 00:39:10
  • What is a Primary Key and what is its purpose?
    What is a Primary Key and what is its purpose?
    Aprimarykeyensuresuniqueidentificationofrecords,supportstablerelationships,andimprovesqueryperformance.Ituniquelyidentifieseachrowinatableusingasinglecolumnorcompositekey,disallowingduplicatesandNULLvalues.1.Itenforcesdataintegritybypreventingduplica
    Mysql Tutorial . Database 349 2025-06-19 00:37:50
  • Why is it recommended to use the utf8mb4 character set?
    Why is it recommended to use the utf8mb4 character set?
    MySQL recommends using utf8mb4 character set because it can fully support four-byte characters such as emojis. Traditional utf8 only supports three-byte characters, which will cause errors or garbled codes when storing Emoji or special text. Therefore, if the application involves user input emojis or minority texts, utf8mb4 must be used to ensure the data is stored correctly. For example, the VARCHAR (255) field can store 255 emoji characters normally under utf8mb4. The content will not be lost. It is recommended to set the database table and field character set to utf8mb4. At the same time, the connection layer should also set charset=utf8mb4 to fully support more Unicode characters, including ancient characters, mathematical symbols, musical symbols and rare Chinese characters, but you need to pay attention to utf8mb4.
    Mysql Tutorial . Database 1050 2025-06-19 00:35:41
  • What are Generated Columns and what are their use cases?
    What are Generated Columns and what are their use cases?
    The generated columns are used in the database to automatically calculate values ??based on other list expressions, simplifying queries and improving performance. They avoid repeated complex calculations, such as automatically generating total_price through unit_price and quantity; they can improve the efficiency of querying, such as pre-calculating order_year to accelerate annual filtering; ensure logical consistency between multiple applications, such as unified calculation of after-tax prices; they are divided into two types: virtual (calculating when reading) and storage (calculating when writing), and should be selected based on the use case.
    Mysql Tutorial . Database 650 2025-06-18 00:31:00
  • How do COMMIT and ROLLBACK work?
    How do COMMIT and ROLLBACK work?
    COMMITpermanentlysaveschangesmadeduringatransaction,whileROLLBACKundoesthem.AtransactionisasequenceofSQLoperationstreatedasasingleunittoensuredataintegrity,followingACIDproperties.Forexample,inamoneytransfer,ifoneaccountisdebitedbuttheotherisn'tcredi
    Mysql Tutorial . Database 468 2025-06-18 00:28:41
  • What does LIMIT 10, 5 mean in a MySQL query?
    What does LIMIT 10, 5 mean in a MySQL query?
    LIMIT10,5meansskipthefirst10rowsandreturnthenext5rows.Thissyntaxisusedforpaginationwherethefirstnumberistheoffset(rowstoskip)andthesecondisthecount(rowstoreturn).ItisusefulfordisplayingdatainpagessuchasPage1:LIMIT0,5,Page2:LIMIT5,5,andsoon.Commonusec
    Mysql Tutorial . Database 436 2025-06-18 00:28:11
  • Is it always better to set the max_connections parameter higher?
    Is it always better to set the max_connections parameter higher?
    Improving max_connections is not always better. Blindly raising it up will lead to resource contention and performance degradation. max_connections is a parameter that limits the number of simultaneous connections in the database. Each connection occupies memory and CPU. If it is set too high, it may exhaust resources. If it is too low, it may limit concurrency. Reasons for not being able to be raised blindly include: 1. Each connection consumes resources; 2. Too many connections cause competition and waiting; 3. Restricted by system file descriptors and thread count; 4. It is difficult to run stably without a connection pool. Reasonable setup methods include: 1. Evaluate connection requirements based on load; 2. Use connection pools to reduce direct connections; 3. Monitor system resource bottlenecks; 4. Distinguish between active and idle connections. Suitable cases for raising the height are: 1. The connection pool is not used and concurrent
    Mysql Tutorial . Database 599 2025-06-18 00:26:11
  • How does semi-synchronous replication work in MySQL?
    How does semi-synchronous replication work in MySQL?
    MySQL's semi-synchronousreplication balances performance with data security by ensuring at least one replica receives transactions. 1. When the transaction is submitted, the master server waits for at least one replica to confirm receipt and writes the relay log; 2. Once confirmed, the master server submits the transaction and returns it to the client successfully; 3. If the timeout does not receive a response, it will automatically fall back to asynchronous mode to maintain the system operation; 4. Enable this function requires installing the plug-in on the master and slave server and setting the corresponding parameters; 5. Its advantage is that it provides stronger data integrity than asynchronous replication, but has slight performance loss and network latency impact. This replication method is suitable for scenarios where high data consistency is required but cannot accept full synchronization performance overhead.
    Mysql Tutorial . Database 873 2025-06-18 00:24:01
  • What is Index Condition Pushdown (ICP)?
    What is Index Condition Pushdown (ICP)?
    IndexConditionPushdown(ICP)isaMySQLoptimizationthatimprovesqueryperformancebypushingWHEREclauseconditionsintothestorageengine.ICPworksbyallowingthestorageenginetoevaluatepartsoftheWHEREconditionduringindexscanning,reducingunnecessaryrowlookupsanddisk
    Mysql Tutorial . Database 158 2025-06-18 00:23:01
  • What are Window Functions and how to use the OVER() clause?
    What are Window Functions and how to use the OVER() clause?
    Window functions are tools in SQL that are used to calculate data while preserving the original row. Common usages include defining window scopes with the OVER() clause. For example, use AVG (salary)OVER (PARTITIONBYdepartment) to calculate the average salary of the department, or use ROW_NUMBER(), RANK(), etc. to rank. 1. The window function groups data through PARTITIONBY, such as calculating the average value by department grouping; 2. Use ORDERBY to sort in the window and combine FRAMEclause to define window frames, such as adding the cumulative sum from the first row to the current row; 3. Common scenarios include grouping statistics retention details, ranking functions and moving average calculations,
    Mysql Tutorial . Database 506 2025-06-18 00:22:31

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