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Technical Articles

Database

Mysql Tutorial

Optimizing MySQL query performance with indexes

The core reason why indexing can improve the speed of MySQL query is that it avoids full table scanning through a directory structure, thereby quickly locates data pages. 1. Indexes reduce data scanning like directories, especially for WHERE, JOIN, and ORDERBY operations; 2. Not all scenarios are applicable. Too many indexes will take up space, reduce write speed, and may mislead the optimizer; 3. Determine whether you need to add an index, you can view the type (ref/range/const as hit), key (displaying index) and rows in the execution plan through the EXPLAIN command; 4. Scenarios that often need to add an index include WHERE conditional column, JOIN connection column, ORDERBY and GROUP

Jul 02, 2025 pm 03:35 PM

mysql index

Handling large BLOB/TEXT data efficiently in MySQL

MySQL is prone to encounter performance bottlenecks when processing large-capacity BLOB and TEXT data, and requires a variety of optimization strategies. 1. Avoid frequent query of large fields, only specify field name query when needed or split large fields into separate tables and associate with foreign keys. 2. Choose the appropriate field type according to actual needs, such as TINYTEXT, MEDIUMTEXT or VARCHAR, and avoid blindly using the maximum capacity type. 3. Pay attention to the performance impact of temporary tables and sorting, avoid sorting or grouping large fields, use overwrite index or summary fields instead, and adjust memory parameters appropriately. 4. Use compression and external storage appropriately, enable InnoDB line compression to save space or store large files in the file system, and the database only saves paths.

Jul 02, 2025 pm 03:30 PM

mysql blob

Using stored procedures and functions in MySQL

The main difference between stored procedures and functions is their purpose and call method. 1. A stored procedure can have multiple input and output parameters, which are called using CALL, which is suitable for performing complex operations and returning multiple result sets; 2. The function must return a value, and the parameters can only be input types, which are usually used for calculations in a query. To create stored procedures, you need to use the DELIMITER separator, which contains input, output parameters and process body logic, such as obtaining a name through the user ID; while to create a function, you need to specify the return type, and there cannot be output parameters, such as determining whether the user exists. When using it, you need to pay attention to issues such as permissions, debugging difficulties, version compatibility and performance optimization. Rational use can improve code reuse rate and system maintainability.

Jul 02, 2025 pm 03:30 PM

mysql stored procedure

Using Common Table Expressions (CTEs) in complex MySQL queries

CTE (CommonTableExpression) is a temporary result set used to simplify complex MySQL queries. It is defined by a WITH clause and exists only during the execution of a single query. It is often used to improve readability, handle recursive queries, and reuse logic. 1. The basic structure of CTE is: WITHcte_nameAS (query definition), followed by the main query; 2. Suitable for multi-layer nesting, duplicate subqueries or scenes requiring modular logic; 3. Support recursive queries, suitable for processing hierarchical data, such as organizational structure, whose structure contains basic query and recursive parts, and uses UNIONALL connection; 4. Pay attention to avoid infinite loops and is limited by the depth of recursive MySQL; 5. Although it is not as good as index optimization JOI

Jul 02, 2025 pm 03:27 PM

mysql CTE

Troubleshooting MySQL error 1045 (Access denied)

MySQL error 1045 (Accessdenied) is usually caused by incorrect username, password, or improper permission settings. 1. First, confirm whether the entered username and password are correct, pay attention to case sensitivity, and check whether there are any spelling errors in the configuration file; 2. Make sure that the user permission allows remote or local connections, you can view it through SELECTUser and HostFROMmysql.user, and create a new user that allows remote connections and authorize it if necessary; 3. Check the bind-address settings in the MySQL configuration file to ensure that its binding address is consistent with the access requirements, such as 0.0.0.0 allows external connections; 4. Troubleshoot other factors, including operating system user authentication methods and MySQL services

Jul 02, 2025 pm 03:25 PM

mysql error Access denied

Comparing InnoDB and MyISAM storage engines in MySQL

InnoDB should be used in scenarios that require transaction support, row-level locks, data integrity and foreign key constraints. MyISAM is suitable for read-intensive and transaction-free scenarios. 1. If ACID compliance and transaction processing are required, such as banking systems, InnoDB should be selected; 2. If concurrent write operations are frequent, InnoDB's row-level lock is better than MyISAM's table-level lock; 3. If reading is mainly used and the data is static, MyISAM has better performance, but if there are many write operations, InnoDB should be selected; 4. If foreign keys or modern full-text search functions are required, InnoDB is the first choice, although MyISAM still has advantages in certain specific full-text search scenarios.

Jul 02, 2025 pm 03:22 PM

mysql storage engine

Troubleshooting common MySQL errors and solutions

Common MySQL errors include connection failure, SQL syntax error, startup failure, etc. When you cannot connect, first confirm whether MySQL is running, whether the port is open, whether the access permissions are correct, and whether the bind-address configuration is reasonable; SQL error 1064 or 1054 requires checking whether the syntax and field exist, and use tools to assist in verification; if the startup fails, you should check the error log, check the data directory permissions, handle the PID file remaining or InnoDB corruption; other problems such as foreign key constraint failure, full table, and excessive connections exceeding the limit also need to be dealt with in a targeted manner.

Jul 02, 2025 pm 03:20 PM

Troubleshooting mysql error

Troubleshooting MySQL high CPU usage issues

MySQL's CPU occupancy is usually caused by slow queries, improper configuration or resource competition. It is necessary to check from the following aspects: 1. Check whether there are slow queries being executed, and use SHOWPROCESSLIST and slow queries log location time-consuming SQL; 2. Analyze and optimize the database structure and index to ensure that frequent query fields have index support to avoid index failure caused by function operations; 3. Check whether MySQL configuration is reasonable, such as innodb_buffer_pool_size, max_connections and other parameters, and evaluate with tools such as mysqltuner.pl; 4. Monitor system resources and load conditions, and exclude CPU usage by other services or timing tasks.

Jul 02, 2025 pm 03:17 PM

mysql cpu usage

Using and interpreting MySQL Performance Schema

MySQL's PerformanceSchema is a built-in database engine for monitoring MySQL's internal runtime performance information. The enable method is as follows: 1. The default majority of versions are enabled, and you can check the status by SHOWVARIABLESLIKE' performance_schema'; 2. If OFF, add performance_schema=ON in the [mysqld] part of my.cnf or my.ini, and restart takes effect; 3. Note that the old version may need to be compiled and enabled manually. Common monitoring tables include: 1. events_statements_summary_by_digest is used to locate the most expensive

Jul 02, 2025 pm 03:04 PM

Debugging MySQL replication slave lag issues

To resolve the problem of MySQL master-slave replication delay, follow the steps to troubleshoot. 1. First check the status of the slave library, execute SHOWSLAVESTATUS\G, confirm that Slave_IO_Running and Slave_SQL_Running are Yes, observe whether the Seconds_Behind_Master value continues to increase and check whether there are errors in Last_Error. 2. Troubleshoot the load and network problems of the main library. Parallel replication can be enabled iftop when the main library has high write pressure; iftop detection can be used; high disk IO of the main library or serious lock competition will also affect the synchronization speed. 3. Check the performance bottleneck of the library, including CPU usage, disk IO status, missing table structure index, large transaction accumulation, etc.

Jul 02, 2025 pm 03:03 PM

mysql copy Delayed debugging

Using window functions in MySQL 8.0 for advanced analytics

MySQL 8.0 introduces window functions, simplifying complex queries. 1. The window function returns statistical values ??for each row and retains the original data; 2. Common functions include ROW_NUMBER(), RANK(), DENSE_RANK(), SUM(), AVG(), etc.; 3. It can be used to rank by category, sum up, and obtain grouped head and tail records; 4. Usage techniques include clarifying PARTITIONBY, ORDERBY and window range settings, and paying attention to index optimization performance.

Jul 02, 2025 pm 02:56 PM

Choosing the right MySQL data types for efficiency

Choosing the right MySQL data type directly affects storage efficiency and query performance. 1. Try to use smaller types, such as TINYINT instead of INT, strings are selected according to length, and DATETIME or DATE are preferred; 2. Clearly set NOTNULL to improve indexing efficiency, if the mobile phone number is set to VARCHAR(20)NOTNULLDEFAULT'', use NOTNULLDEFAULTCURRENT_TIMESTAMP when creating time; 3. Use TEXT/BLOB type with caution to avoid frequent use in query conditions. When the data volume is large, it should be split into separate tables and matched with the full text index; 4. Use ENUM and SET types reasonably

Jul 02, 2025 pm 02:49 PM

mysql workbench table data import wizard error

When encountering MySQLWorkbenchTableDataImportWizard error, the common causes and solutions are as follows: 1. File path or permission problem, check whether the path is correct, avoid special characters, and ensure that there is read permission; 2. Data format does not match, confirm the field type, order and null value processing method, and you can first import the temporary table to clean the data; 3. Encoding format problem, select the character set consistent with the file or convert it to UTF-8; 4. Ignore the first row and column name, separator setting error, or failure caused by large files, pay attention to check the column name option, adjust the separator, and split the large file, or import it using command line tools.

Jul 01, 2025 am 01:44 AM

mysql access denied for user root@localhost

Accessdeniedforuser'root'@'localhost' is usually caused by password errors, insufficient permissions, user binding problems or configuration files. The specific solutions are as follows: 1. Confirm whether the password is correct or try to log in with empty password and set a new password; 2. If the permissions are insufficient, you can enter safe mode to reset the password and update the permissions; 3. Check whether the corresponding host of the user matches the connection method, and manually create and authorize the user if necessary; 4. Check the configuration file and authentication plug-in to ensure that skip-name-resolve is not enabled or the correct authentication plug-in is used.

Jul 01, 2025 am 01:43 AM