国产av日韩一区二区三区精品,成人性爱视频在线观看,国产,欧美,日韩,一区,www.成色av久久成人,2222eeee成人天堂

current location：Home > Technical Articles > Daily Programming > Mysql Knowledge

  • How to check the MySQL server version?
    How to check the MySQL server version?
    To view the MySQL server version, it can be implemented in various ways, as follows: 1. Execute mysql-V using the command line; 2. Log in to the MySQL client and run SELECTVERSION(); or enter status; (abbreviated as \s); 3. Execute SHOWVARIABLESLIKE'version'; obtain more accurate version information; 4. Execute SQL query version number through database connection in the program, as shown in the Python sample code.
    Mysql Tutorial . Database 955 2025-06-20 00:59:31
  • How to use the CASE WHEN statement in a query?
    How to use the CASE WHEN statement in a query?
    TheSQLCASEWHENstatementisusedtohandleconditionallogicinqueriesbyreturningdifferentresultsbasedonspecifiedconditions.Itfunctionslikeanif-elsestatementandcanbeappliedinSELECT,WHERE,ORDERBY,andHAVINGclauses.Forexample,itcanclassifysalesas“Low”,“Medium”,
    Mysql Tutorial . Database 892 2025-06-20 00:59:11
  • What are the roles of the redo log and undo log in InnoDB?
    What are the roles of the redo log and undo log in InnoDB?
    InnoDB's redolog and undolog guarantee the persistence, atomicity and MVCC of transactions respectively. Redolog is a physical log that is written before data modification, records data page changes, supports crash recovery, and uses loop writing to improve performance; Undolog is a logical log that records reverse operations, is used for transaction rollback and implementation of MVCC, organizes multi-version data snapshots through linked lists, and is cleaned by purge threads. The two work together to ensure the complete implementation of transaction ACID characteristics.
    Mysql Tutorial . Database 292 2025-06-20 00:58:31
  • What types of locks does MySQL use, like table locks, row locks, and gap locks?
    What types of locks does MySQL use, like table locks, row locks, and gap locks?
    MySQL manages concurrent access using table locks, row locks, and gap locks. Table locks lock the entire table, suitable for scenarios with more reads and fewer writes; row locks allow multiple transactions to operate different rows, improving concurrency; gap locks prevent phantom reading and lock index gaps. These three locks work according to different storage engines and isolation levels.
    Mysql Tutorial . Database 789 2025-06-20 00:55:50
  • How to check the current number of connections and server status?
    How to check the current number of connections and server status?
    To view the current number of connections and server status, you can use the following methods: 1. View the number of server connections: Use ss or netstat commands, such as ss-tuln or netstat-tuln to list the listening ports, and combine ss-tn|wc-l to count the number of TCP connections; 2. Monitor the overall status of the server: use uptime to view the load and runtime, and use top and htop to view the CPU and memory usage in real time; 3. Use monitoring tools to achieve long-term observation: Deploy Grafana Prometheus, Netdata or Zabbix to graphically display data and set alarms; 4. Notes: Handle TIME_WAIT status connection, optimize kernel parameters and query different commands
    Mysql Tutorial . Database 149 2025-06-20 00:55:31
  • What is the functional difference between the WHERE and HAVING clauses?
    What is the functional difference between the WHERE and HAVING clauses?
    In SQL, the main difference between WHERE and HAVING is the execution timing and the type of data filtered. 1.WHERE filters a single row before grouping, and cannot use an aggregation function; 2.HAVING filters the aggregation results after grouping, allowing the use of an aggregation function. For example, when querying departments with more than 10 high-paying employees, WHERE first filters low-paying employees, then uses GROUPBY to group them, and finally uses HAVING to filter groups that meet the criteria. In terms of performance, WHERE should be used to reduce the amount of data, and HAVING should only be used when filtering the aggregate results.
    Mysql Tutorial . Database 856 2025-06-20 00:55:11
  • Which is more efficient: COUNT(*), COUNT(1), or COUNT(column_name)?
    Which is more efficient: COUNT(*), COUNT(1), or COUNT(column_name)?
    InmodernSQLdatabases,COUNT(),COUNT(1),andCOUNT(column_name)havelittletonoperformancedifferenceinbasicqueries.1.COUNT()countsallrows,includingNULLs,andisbestfortotalrowcount.2.COUNT(1)behavesthesameasCOUNT(),withnoperformanceadvantage,andisusedmainlyb
    Mysql Tutorial . Database 276 2025-06-20 00:53:51
  • What are optimistic and pessimistic locks, and how to implement them in MySQL?
    What are optimistic and pessimistic locks, and how to implement them in MySQL?
    Pessimistic locks and optimistic locks are two strategies for handling concurrent database access. Pessimistic locking assumes conflicts and locks are immediately added when the data is modified, such as in MySQL using SELECT...FORUPDATE or SELECT...LOCKINSHAREMODE, which is suitable for high-competitive scenarios but may degrade performance. Optimistic locks assume fewer conflicts and do not lock immediately, but check version numbers or timestamps when updated. They are suitable for low-competitive scenarios and avoid lock overhead, but the application layer needs to handle conflicts. If you choose a pessimistic lock, if you write frequently and have high data consistency requirements; if you choose an optimistic lock, if you have fewer conflicts, you hope to improve concurrency and can handle it elegantly. In addition, pessimistic locks may lead to deadlocks, and optimistic locks require additional logic to handle conflicts.
    Mysql Tutorial . Database 894 2025-06-20 00:51:20
  • What is read-write splitting and how is it implemented?
    What is read-write splitting and how is it implemented?
    Read-writesplittingimprovesdatabaseperformancebyseparatingreadandwriteoperationsacrossdifferentservers.Itworksbydirectingwritestotheprimarydatabaseandreadstoreplicas,reducingload,improvingresponsetime,andenhancingfaulttolerance.Commonimplementationme
    Mysql Tutorial . Database 261 2025-06-20 00:37:31
  • How to design a database sharding strategy?
    How to design a database sharding strategy?
    The core of designing a database sharding strategy is "how to reasonably separate the data without affecting use". The key points include: 1. Select the right shard key, and fields such as user ID that are high-base, evenly distributed and commonly used as query conditions should be selected, such as user ID, to avoid using time or high-frequency query fields to prevent hot spots and cross-slicing problems; 2. Control the number of shards, set to 16 or 32 in the initial stage, and reasonably estimate the total data volume and node bearing capacity to avoid operation and maintenance or expansion problems caused by too much or too little; 3. Optimize query and transactions, reduce cross-slicing queries, use redundancy or intermediate layer aggregation to improve efficiency, pay attention to the limited transaction support in the shard environment, and it is necessary to cooperate with cache or secondary index to optimize query performance, report statistics and other operations, and it is recommended to process in parallel at the application layer to reduce database pressure.
    Mysql Tutorial . Database 640 2025-06-20 00:35:31
  • What is a subquery and does it affect performance?
    What is a subquery and does it affect performance?
    Asubquerycanaffectperformancedependingonitsusage.1.Correlatedsubqueriesmayexecuterepeatedly,onceforeachrowintheouterquery.2.Poorlywrittensubqueriescanpreventefficientindexuse.3.Subqueriesaddcomplexity,makingqueryoptimizationharder.However,moderndatab
    Mysql Tutorial . Database 660 2025-06-20 00:17:40
  • What is a typical process for MySQL master failover?
    What is a typical process for MySQL master failover?
    MySQL main library failover mainly includes four steps. 1. Fault detection: Regularly check the main library process, connection status and simple query to determine whether it is downtime, set up a retry mechanism to avoid misjudgment, and can use tools such as MHA, Orchestrator or Keepalived to assist in detection; 2. Select the new main library: select the most suitable slave library to replace it according to the data synchronization progress (Seconds_Behind_Master), binlog data integrity, network delay and load conditions, and perform data compensation or manual intervention if necessary; 3. Switch topology: Point other slave libraries to the new master library, execute RESETMASTER or enable GTID, update the VIP, DNS or proxy configuration to
    Mysql Tutorial . Database 382 2025-06-19 01:06:41
  • What is MySQL Group Replication (MGR)?
    What is MySQL Group Replication (MGR)?
    MySQLGroupReplication (MGR) is a plug-in high-availability clustering technology officially provided by MySQL, which is based on the Paxos protocol to achieve strong data consistency and automatic failover. 1. MGR synchronizes transaction logs and authenticates them among multiple nodes through the group communication system to ensure data consistency; 2. Its core features include automatic failover, multiple write/single-write mode optional, and built-in conflict detection mechanism; 3. Deployment requires at least three nodes, and configures key parameters such as GTID, row format log, and unique server_id; 4. Common processes include preparing servers, configuring parameters, initializing nodes, joining clusters and status checks. MGR is suitable for scenarios with high data consistency requirements, but is sensitive to network latency
    Mysql Tutorial . Database 234 2025-06-19 01:06:20
  • How to connect to a MySQL database using the command line?
    How to connect to a MySQL database using the command line?
    The steps to connect to the MySQL database are as follows: 1. Use the basic command format mysql-u username-p-h host address to connect, enter the username and password to log in; 2. If you need to directly enter the specified database, you can add the database name after the command, such as mysql-uroot-pmyproject; 3. If the port is not the default 3306, you need to add the -P parameter to specify the port number, such as mysql-uroot-p-h192.168.1.100-P3307; In addition, if you encounter a password error, you can re-enter it. If the connection fails, check the network, firewall or permission settings. If the client is missing, you can install mysql-client on Linux through the package manager. Master these commands
    Mysql Tutorial . Database 972 2025-06-19 01:05:41

Tool Recommendations

jQuery enterprise message form contact code

jQuery enterprise message form contact code is a simple and practical enterprise message form and contact us introduction page code.
form button
2024-02-29

HTML5 MP3 music box playback effects

HTML5 MP3 music box playback special effect is an mp3 music player based on HTML5 css3 to create cute music box emoticons and click the switch button.

HTML5 cool particle animation navigation menu special effects

HTML5 cool particle animation navigation menu special effect is a special effect that changes color when the navigation menu is hovered by the mouse.
Menu navigation
2024-02-29

jQuery visual form drag and drop editing code

jQuery visual form drag and drop editing code is a visual form based on jQuery and bootstrap framework.
form button
2024-02-29

Organic fruit and vegetable supplier web template Bootstrap5

An organic fruit and vegetable supplier web template-Bootstrap5
Bootstrap template
2023-02-03

Bootstrap3 multifunctional data information background management responsive web page template-Novus

Bootstrap3 multifunctional data information background management responsive web page template-Novus
backend template
2023-02-02

Real estate resource service platform web page template Bootstrap5

Real estate resource service platform web page template Bootstrap5
Bootstrap template
2023-02-02

Simple resume information web template Bootstrap4

Simple resume information web template Bootstrap4
Bootstrap template
2023-02-02

Cute summer elements vector material (EPS PNG)

This is a cute summer element vector material, including the sun, sun hat, coconut tree, bikini, airplane, watermelon, ice cream, ice cream, cold drink, swimming ring, flip-flops, pineapple, conch, shell, starfish, crab, Lemons, sunscreen, sunglasses, etc., the materials are provided in EPS and PNG formats, including JPG previews.
PNG material
2024-05-09

Four red 2023 graduation badges vector material (AI EPS PNG)

This is a red 2023 graduation badge vector material, four in total, available in AI, EPS and PNG formats, including JPG preview.
PNG material
2024-02-29

Singing bird and cart filled with flowers design spring banner vector material (AI EPS)

This is a spring banner vector material designed with singing birds and a cart full of flowers. It is available in AI and EPS formats, including JPG preview.
banner picture
2024-02-29

Golden graduation cap vector material (EPS PNG)

This is a golden graduation cap vector material, available in EPS and PNG formats, including JPG preview.
PNG material
2024-02-27

Home Decor Cleaning and Repair Service Company Website Template

Home Decoration Cleaning and Maintenance Service Company Website Template is a website template download suitable for promotional websites that provide home decoration, cleaning, maintenance and other service organizations. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-05-09

Fresh color personal resume guide page template

Fresh color matching personal job application resume guide page template is a personal job search resume work display guide page web template download suitable for fresh color matching style. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-02-29

Designer Creative Job Resume Web Template

Designer Creative Job Resume Web Template is a downloadable web template for personal job resume display suitable for various designer positions. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-02-28

Modern engineering construction company website template

The modern engineering and construction company website template is a downloadable website template suitable for promotion of the engineering and construction service industry. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-02-28