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  • mysql get year from date
    mysql get year from date
    You can use the YEAR() function to extract years in MySQL. 1. Use YEAR (date_column) to extract years from DATE, DATETIME or TIMESTAMP type fields; 2. It is often used to count the annual data volume, group by year, or filter specific year records; 3. Use WHEREYEAR (date_column)=year to filter data, but may affect index performance; 4. It is recommended to replace it with range query to improve efficiency, such as WHEREdate_column>='YYYY-01-01'ANDdate_column
    Mysql Tutorial . Database 435 2025-07-10 12:10:50
  • Leveraging the MySQL Slow Query Log for Tuning
    Leveraging the MySQL Slow Query Log for Tuning
    MySQL's slow query log is an important tool for optimizing database performance. It helps locate performance bottlenecks by recording SQL statements whose execution time exceeds a specified threshold. 1. Enable slow query log to set slow_query_log, slow_query_log_file and long_query_time parameters in the configuration file; 2. Use mysqldumpslow or pt-query-digest tools to analyze logs, and pay attention to key fields such as Query_time, Lock_time, Rows_sent and Rows_examined; 3. Common problems include the lack of indexing that leads to full table scanning, unreasonable query design, and sorting
    Mysql Tutorial . Database 599 2025-07-10 11:50:31
  • Analyzing MySQL buffer pool usage for tuning
    Analyzing MySQL buffer pool usage for tuning
    MySQL bufferpool usage analysis is the key to tuning, which directly affects read and write performance. 1. You can view the total size, usage and number of free pages through SHOWENGINEINNODBSTATUS\G; 2. Query the INNODB_BUFFER_POOL_STATS table of information_schema to obtain structured data, such as idle rate, data page proportion, and dirty page proportion; 3. The higher the hit rate, the better, OLTP needs a higher hit rate, and it is normal to have a lower OLAP scenario. The calculation formula is 1-(reads/read_requests), and below 95% may require optimization of query or increase buffer
    Mysql Tutorial . Database 687 2025-07-10 11:37:31
  • how to call a stored procedure in mysql
    how to call a stored procedure in mysql
    The key to calling MySQL stored procedures is to clarify the stored procedure name and parameters, and use CALL statements or programming interfaces to call. 1. Use CALL statement to call directly: such as CALLget_user_info(123); when multi-parameters, you need to fill in order and pay attention to type matching; 2. Call in client tools: such as MySQLWorkbench executes CALL statement, if there is no return value, you can check data changes or log confirmation effect; 3. Process output parameters: define the results received by user variables, such as CALLget_total_orders(1,@total); SELECT@total; 4. Call from program code: such as Python using cursor.
    Mysql Tutorial . Database 253 2025-07-10 11:33:01
  • mysql create temporary table
    mysql create temporary table
    A temporary table is a temporary table structure created in the current database connection and is automatically deleted after disconnection. It is suitable for saving intermediate results in complex queries, report generation or step-by-step calculations, improving execution efficiency. 1. The creation syntax is CREATETEMPORARYTABLEtemp_table_name(...) or quickly create based on query results; 2. When using it, you need to pay attention to only the current session is accessible, triggers and foreign keys are not supported, ordinary tables with the same name may be overwritten, and frequent and extensive use is avoided; 3. Typical scenarios include intermediate result sets, pagination summary, data statistics of multiple references, and data cleaning.
    Mysql Tutorial . Database 336 2025-07-10 11:14:41
  • mysql insert on duplicate key update
    mysql insert on duplicate key update
    INSERT...ONDUPLICATEKEYUPDATE is a statement in MySQL that performs insertion or update operations when repeated key conflicts are handled. Its core mechanism is: if the insertion data does not violate the primary key or unique constraint, it will be inserted normally; if it conflicts, the update part will be executed. This statement is suitable for user registration, order writing and other scenarios, and can simplify logic and ensure data integrity. Key points of use include: 1. The table must define a primary key or a unique index; 2. The update of multiple fields must be separated by commas; 3. The insertion value can be referenced through the VALUES() function; 4. Support inserting multiple rows at a time, and each row independently determines whether to update. Notes include: Ensure the index is accurate to avoid misinterpretation, pay attention to lock performance under high concurrency, and use transaction control reasonably
    Mysql Tutorial . Database 839 2025-07-10 11:11:10
  • mysql error 1045 access denied for user 'root'@'localhost'
    mysql error 1045 access denied for user 'root'@'localhost'
    I encountered MySQL error 1045: Accessdeniedforuser'root'@'localhost', indicating that authentication failed when connecting to the database. Common reasons and solutions are as follows: 1. Check whether the user name and password are correct. It is recommended to use sudomysql-uroot to log in without password; 2. Confirm that the MySQL service has been started, and you can check and start the service through systemctl or brewservices; 3. Check the permission configuration, confirm the bind-address and skip-networking settings, and ensure that the root user is allowed to log in from the corresponding host; 4. If you forget your password, you can deactivate MySQL and
    Mysql Tutorial . Database 397 2025-07-09 02:07:01
  • mysql show grants for user
    mysql show grants for user
    To view MySQL user permissions, use the SHOWGRANTS command, the syntax is SHOWGRANTSFOR'user'@'hostname'; for example, SHOWGRANTSFOR'test_user'@'localhost'; you can view the local connection user permissions; if the host name is not determined, you can use % wildcard instead. In the execution results, USAGE means no actual permissions, SELECT, INSERT, etc. are common operation permissions, and the content after ON indicates the scope of the permissions, such as mydb.* means all objects under the mydb database. This command is suitable for troubleshooting permission problems, permission migration and copying, and avoiding misdeletion of permissions. Notes include: The username and master must be matched accurately
    Mysql Tutorial . Database 697 2025-07-09 01:59:11
  • how to simulate full outer join in mysql
    how to simulate full outer join in mysql
    MySQL does not support FULLOUTERJOIN, and can be implemented through LEFTJOIN and RIGHTJOIN combined with UNION. 1. Use LEFTJOIN and RIGHTJOIN joint query, merge and deduplication through UNION, pay attention to the consistent order of the fields; 2. Use COALESCE to unify the primary key when processing duplicate data, which is convenient for subsequent processing; 3. For complex scenarios, temporary tables or subqueries can be used to process the left and right table data separately and then merge them to improve readability. The core is to merge left and right results and remove heavy weights.
    Mysql Tutorial . Database 482 2025-07-09 01:56:41
  • mysql too many connections error
    mysql too many connections error
    When MySQL error occurs, the following steps can be solved through the following steps: 1. Log in to MySQL to execute SHOWSTATUSLIKE'Threads_connected' and SHOWVARIABLESLIKE'max_connections' to confirm whether the number of connections exceeds the limit; 2. Check whether there is a prompt for "Toomyconnections" in the log; 3. Temporarily increase the max_connections value and take effect by dynamically setting or modifying the configuration file; 4. Check PROCESSLIST and KILL to release idle connections; 5. Long-term optimization includes reasonably configuring the connection pool parameters,
    Mysql Tutorial . Database 405 2025-07-09 01:55:40
  • mysql self join example
    mysql self join example
    SelfJoin is a technology in MySQL that connects the same table to itself through alias. It is often used to process hierarchical or parent-child relationship data. For example, in the employees table, use LEFTJOIN to associate employees with their boss information: SELECTe.nameASemployee_name,m.nameASmanager_nameFROMemployeeseLEFTJOINemployeeesmONe.manager_id=m.id; this query can obtain the name of each employee and his direct boss, which is suitable for organizational structure, recursive data and other scenarios. Pay attention to using alias, avoid circular references and optimize performance.
    Mysql Tutorial . Database 741 2025-07-09 01:45:20
  • mysql create read only user
    mysql create read only user
    The steps to create a read-only user are as follows: 1. Create a user with the CREATEUSER command, 2. GRANT command grant SELECT permissions, 3. Specify the accessed database and tables, 4. Perform FLUSHPRIVILEGES to ensure that the permissions take effect; to improve security, you can restrict visible fields through view or combine the application layer desensitization process; common problems need to be avoided such as mis-granting other permissions, not recycling of unnecessary permissions, not refreshing permissions, and improper host settings. It is recommended to check the user permissions after operation to ensure the configuration is correct.
    Mysql Tutorial . Database 762 2025-07-09 01:44:40
  • Defining Effective Primary Keys in MySQL Tables
    Defining Effective Primary Keys in MySQL Tables
    The primary key is a field or combination that uniquely identifies records in a database table. Four principles must be followed when selecting: 1. Priority is given to using self-incremental integers such as INT or BIGINT to improve efficiency; 2. Avoid long strings such as UUID or mailboxes to avoid affecting performance; 3. Use business fields with caution, such as ID number due to poor stability; 4. Try not to use composite primary keys to maintain due to their complexity. At the same time, pay attention to the self-value-added configuration, delete the ID and do not recycle it, and do not manually insert the self-added field.
    Mysql Tutorial . Database 297 2025-07-09 01:41:50
  • How to Install MySQL Server on Linux
    How to Install MySQL Server on Linux
    The steps to install MySQL server on Linux include confirming the system environment, selecting the installation source, executing installation commands, and initializing settings. First, update the system software package, Ubuntu uses aptupdate&&aptgrade, and CentOS uses yumupdate; secondly, add official source options, Ubuntu downloads and installs the mysql-apt-config package and updates the source list, and CentOS installs the official rpm package; then executes the installation through aptinstallmysql-server or yuminstallmysql-server; then starts the service and sets the boot boot, and runs mysq
    Mysql Tutorial . Database 717 2025-07-09 01:32:21

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