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  • mysql now() vs current_timestamp()
    mysql now() vs current_timestamp()
    The main difference between NOW() and CURRENT_TIMESTAMP() is in the usage scenario; CURRENT_TIMESTAMP can be used as the column default value and automatically update keywords, while NOW() is only a function; both return the same result in the query, but when defining the table structure, you must use CURRENT_TIMESTAMP to set the default value or automatically update the timestamp.
    Mysql Tutorial . Database 494 2025-07-14 01:23:21
  • Connecting External Applications to MySQL Databases
    Connecting External Applications to MySQL Databases
    ToconnectexternalapplicationstoMySQLsecurely,firstenableremoteaccessbychangingthebind-addressto0.0.0.0inmy.cnf/my.ini,thengrantremoteaccessviaGRANTcommandandflushprivileges.2)Ensurethefirewallallowstrafficonport3306.3)Usethecorrectconnectionstringiny
    Mysql Tutorial . Database 828 2025-07-14 01:16:41
  • mysql command line client tips
    mysql command line client tips
    Mastering common techniques of MySQL command line can improve operation efficiency; configuring default login information can quickly enter the database interface; using up and down keys or systemhistory to view historical commands, the Tab key will automatically complete the table name field; using \G vertically display results and pagermore pagination display; using shortcut commands such as \s to view connection status, \c cancel statement, \g execution statement, and \h to obtain help documents.
    Mysql Tutorial . Database 149 2025-07-14 01:01:21
  • Best practices for designing relational schemas in MySQL
    Best practices for designing relational schemas in MySQL
    The key to designing the MySQL database model lies in clear logic and reasonable structure, which directly affects query efficiency and maintenance costs. 1. Correctly use primary and foreign key constraints to ensure data integrity and avoid orphan records; 2. Reasonably select field types and lengths to save storage space and improve performance; 3. Establish appropriate indexes to improve query speed, but avoid abuse; 4. Balance normalization and anti-normalization, taking into account consistency and query performance.
    Mysql Tutorial . Database 151 2025-07-14 00:49:31
  • mysql error 1062 duplicate entry for key
    mysql error 1062 duplicate entry for key
    The "Duplicateentryforkey" error appears because a uniqueness constraint is violated when inserting or updating the data. "xxx" in MySQL error message indicates an existing value, and "yyy" is the conflicting index name. For example, duplication of username causes users.username to conflict. Common scenarios include duplicate usernames of the registration system, product number conflicts, manual insertion errors of self-increasing IDs, etc. The processing methods are: ? First check to confirm whether there is a record;? Use ONDUPLICATEKEYUPDATE to update if there is an existence; ?In the program, check or catch an exception in advance to prompt the user to modify it. Avoiding methods include clarifying unique index fields during the design stage, applying layer verification and logging during use. Misoperation
    Mysql Tutorial . Database 344 2025-07-14 00:32:51
  • Approaches to Sharding Data in MySQL Databases
    Approaches to Sharding Data in MySQL Databases
    MySQL database sharding is an effective way to scale large data sets and handle high traffic loads. 1. Vertical shards divide data according to table or functional boundaries, which is suitable for scenarios where module separation, access mode differences or sensitive data need to be isolated; 2. Horizontal shards distribute table rows to different servers, and achieve balancing load through scope, hash or directory strategies, which is suitable for large table splitting; 3. Directory shards use lookup table dynamic mapping keys to shards, providing flexible expansion capabilities but increasing management complexity; 4. Mixed models combine vertical and horizontal shards to customize strategies according to data access mode to improve overall scalability. Choosing a suitable sharding solution should be based on data growth trends and query behaviors to avoid early over-design.
    Mysql Tutorial . Database 724 2025-07-14 00:20:21
  • Choosing Appropriate Data Types in MySQL
    Choosing Appropriate Data Types in MySQL
    Selecting the right data type in MySQL can improve performance and storage efficiency. 1. Select fixed-length CHAR or variable-length VARCHAR according to the field length, and use TINYINT in the status field first; 2. Use DATE, DATETIME or TIMESTAMP as required for the time type to avoid using INT to store timestamps; 3. Use TEXT/BLOB to give priority to VARCHAR to reduce I/O overhead; 4. Use ENUM type or independent table to enumerate values to improve data standardization and query efficiency.
    Mysql Tutorial . Database 299 2025-07-13 02:53:00
  • what is a covering index in mysql
    what is a covering index in mysql
    Overwrite indexes in MySQL are indexes that contain all columns required for a query, thus avoiding access to actual table data. It reduces I/O by eliminating table searches and improves query speed. For example, when SELECTidFROMusersWHEREstatus='active' is executed, if there is a composite index of (status,id), it constitutes an overlay index. The best scenarios for using overlay indexes include: 1. Query involves only a small number of columns; 2. Aggregated queries such as COUNT or SUM; 3. High-frequency conditional queries. To identify an overwrite index opportunity, view the Extra column in the EXPLAIN output. If “Usingindex” is displayed, the overwrite index is used. All the query should be included when designing
    Mysql Tutorial . Database 582 2025-07-13 02:47:50
  • how to create user in mysql
    how to create user in mysql
    To create MySQL users, you need to pay attention to syntax and permission settings. First, use CREATEUSER to specify the user name, host name and password, such as CREATEUSER'testuser'@'localhost'IDENTIFIEDBY'password123'; if you want to allow any IP to log in, change localhost to %. Secondly, the permissions are allocated through the GRANT command, such as GRANTALLPRIVILEGESONtestdb.*TO'testuser'@'localhost'; Common permissions include SELECT, INSERT, UPDATE, DELETE, CREATE, DROP and AL
    Mysql Tutorial . Database 647 2025-07-13 02:47:01
  • mysql user defined functions (udf)
    mysql user defined functions (udf)
    MySQLUDF is a user-defined function written in C/C and compiled into a shared library and registered with MySQL for efficient implementation of specific logic. 1. UDF is suitable for computing operations such as string processing, mathematical operations, etc., and the execution efficiency is higher than that of stored procedures; 2. The creation steps include writing code, compiling into .so files, placing them in MySQL accessible directory, and registering and using them through CREATEFUNCTION; 3. When using them, you need to pay attention to compatibility, stability, debugging difficulty and deployment complexity. It is recommended to only be used when high-performance requirements and SQL is difficult to implement; 4. Alternative solutions include storage functions, triggers, application layer processing or MySQL plug-in system, which can be selected according to actual needs.
    Mysql Tutorial . Database 687 2025-07-13 02:45:20
  • mysql date_add function
    mysql date_add function
    MySQL's DATE_ADD function is used to add a specified time interval to a date or time value. Its basic syntax is DATE_ADD(date,INTERVALexprunit), where date is the original date or time, INTERVAL is the keyword, expr is the increased number, and unit is the time unit such as DAY, MONTH, etc. 1. It is often used to calculate future time points, such as one day's reminder after registration, member validity period, etc.; 2. It can be used in combination with other functions, such as using CURDATE() to obtain yesterday's data, or NOW() to query future appointments; 3. When using it, you need to pay attention to the correctness of the date format, unit spelling, negative number use and cross-month/year boundary issues. Mastering this function helps
    Mysql Tutorial . Database 664 2025-07-13 02:45:01
  • Using the MySQL Shell for administration and scripting
    Using the MySQL Shell for administration and scripting
    The method of MySQLShell to connect to the database is to use the mysqlsh command to start and enter connection information, or directly specify user@host:port on the command line; 1. The startup method is flexible, supports interactive input or directly specifying parameters; 2. Pay attention to SSL settings and authentication methods, especially when remote connections, to ensure the correct permissions and passwords; 3. After entering the shell, it is SQL mode by default, and can perform regular SQL operations; 4. Support switching to JS or Python mode to write complex scripts to realize automated tasks; 5. Script writing requires attention to mode selection, output format, exception handling and file saving; 6. Provide practical tips, such as viewing the current mode, switching paths, multi-instance connections, and checking help articles
    Mysql Tutorial . Database 637 2025-07-13 02:43:51
  • mysql use random order
    mysql use random order
    Using ORDERBYRAND() to implement random sorting is suitable for small data volumes or temporary requirements, but has poor performance. The problem is that the full table scans and generates random numbers for each row and then sorts it, resulting in extremely low efficiency when queries are large data or high-frequency. Alternatives include: 1. Pre-random numbering; 2. Random ID range sampling; 3. Pagination cache; 4. Maintaining random pools separately. Which method to choose depends on business requirements and data structure.
    Mysql Tutorial . Database 785 2025-07-13 02:32:10
  • mysql transaction commit rollback
    mysql transaction commit rollback
    Transactions are the mechanism in MySQL to ensure data consistency, and have ACID characteristics (atomicity, consistency, isolation, and persistence). The core is to ensure that a set of SQL operations are either successful or all failed. commit is used to confirm all changes in the transaction and write to the database, and rollback is used to undo operations in the transaction and restore to the initial state. Note when using: 1. The default automatic commit needs to be closed for manual control; 2. Transactions cannot be nested, but partial rollback can be simulated by save points; 3. Long transactions affect performance as short as possible; 4. DDL statements will implicitly submit transactions; 5. Forgot to commit or the exception is not processed may lead to lock waiting or data inconsistency; 6. Multi-connection operations need to pay attention to transaction independence. Master these
    Mysql Tutorial . Database 228 2025-07-13 02:26:11

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