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  • Analyzing Query Execution with MySQL EXPLAIN
    Analyzing Query Execution with MySQL EXPLAIN
    MySQL's EXPLAIN is a tool used to analyze query execution plans. You can view the execution process by adding EXPLAIN before the SELECT query. 1. The main fields include id, select_type, table, type, key, Extra, etc.; 2. Efficient query needs to pay attention to type (such as const, eq_ref is the best), key (whether to use the appropriate index) and Extra (avoid Usingfilesort and Usingtemporary); 3. Common optimization suggestions: avoid using functions or blurring the leading wildcards for fields, ensure the consistent field types, reasonably set the connection field index, optimize sorting and grouping operations to improve performance and reduce capital
    Mysql Tutorial . Database 982 2025-07-12 02:07:21
  • what is a primary key in mysql
    what is a primary key in mysql
    AprimarykeyinMySQLisaconstraintthatuniquelyidentifieseachrowinatable.1.Itensuresdatauniquenessandnon-nullvalues,eitherinasinglecolumnoracombinationofcolumns.2.Everytableshouldhaveaprimarykeytoenforceentityintegrityandallowreliabledistinctionbetweenre
    Mysql Tutorial . Database 148 2025-07-12 02:06:31
  • mysql error 1215 cannot add foreign key constraint
    mysql error 1215 cannot add foreign key constraint
    MySQL error "Error1215:Cannotaddforeignkeyconstraint" is usually caused by the foreign key setting that does not meet the prerequisites. 1. Data type mismatch: The data type, length, and symbol attributes of the foreign key and the primary key field must be the same; 2. The engine is inconsistent: Only the InnoDB engine supports foreign keys, so make sure that the table uses InnoDB; 3. Different character sets or sorting rules: It is recommended to unify the character set and sorting rules; 4. The field is not indexed: the foreign key field should be explicitly indexed; 5. The table or field name is incorrectly spelled: it is necessary to check whether it exists and whether it is spelled correctly. During the investigation, the above reasons can be corrected one by one.
    Mysql Tutorial . Database 923 2025-07-12 01:59:22
  • Managing user accounts and granular privileges in MySQL
    Managing user accounts and granular privileges in MySQL
    MySQL user permission management must follow the principle of minimum permissions to avoid abuse of root accounts. 1. When creating a user, use the CREATEUSER statement to ensure that there is no permission at the beginning; 2. When authorizing, assign specific permissions such as SELECT and INSERT rather than all permissions as needed; 3. Use GRANT and REVOKE to accurately control and recycle permissions; 4. Check permissions regularly and clean up accounts that are no longer needed; 5. Use wildcards to achieve flexible authorization but use them with caution. These methods can improve database security and reduce risks.
    Mysql Tutorial . Database 325 2025-07-12 01:52:20
  • how to install mysql on ubuntu
    how to install mysql on ubuntu
    The steps to install MySQL on Ubuntu include: 1. Update the system package and install MySQL; 2. Run the secure initialization script to set the root password, disable remote login, etc.; 3. Check the service status and perform basic operations; 4. Handle possible permissions and login problems. First update the package list, execute sudoaptupdate and sudoaptinstallmysql-server to install MySQL, and then configure security options through sudomysql_secure_installation to ensure that strong passwords are set and remote access is disabled according to requirements. After the installation is completed, use the systemctl command to manage the service status and use sudom
    Mysql Tutorial . Database 698 2025-07-12 01:51:11
  • mysql table lock vs row lock
    mysql table lock vs row lock
    Table locks are suitable for low-concurrency, batch operation or maintenance scenarios. For example, when using the MyISAM engine, performing DDL operations or full-table scans, their overhead is small but their concurrency is poor. Row locks are suitable for high-concurrency write scenarios. They are supported by the InnoDB engine. Fine-grained locks are realized through index hits to improve concurrency but may cause deadlocks. When choosing, according to business needs, use InnoDB row locks with more writes and reads, and use MyISAM table locks with less data or mainly reads, and ensure that querying and indexing can avoid lock upgrades.
    Mysql Tutorial . Database 284 2025-07-12 01:48:41
  • mysql composite index example
    mysql composite index example
    MySQL composite index follows the principle of leftmost prefix, and the query condition must include the leftmost column of the index before it can hit the index. 1. The index structure is organized in the order of definition, such as (name, age, city) first sorted by name, and then subdivided in sequence; 2. The hit condition includes continuous combinations starting with the leftmost column, such as WHEREname=... or WHEREname=...ANDage=...; 3. If the leftmost column is not included, it cannot be hit if only age or city is used; 4. When creating, the high-divided and commonly used query fields should be placed in front of it, and redundancy and excessive indexing should be avoided; 5. The use of functions, OR without index support, and fuzzy matching at the beginning of % will cause the index to fail.
    Mysql Tutorial . Database 614 2025-07-12 01:36:01
  • mysql create table syntax
    mysql create table syntax
    The key to creating a MySQL table is to master the basic syntax and common options of CREATETABLE statements. 1. The basic syntax requires specifying field names, data types and constraints, such as NOTNULL, PRIMARYKEY, AUTO_INCREMENT; 2. Common field types include INT, VARCHAR(n), TEXT, DATE, DATETIME, TIMESTAMP and DECIMAL(m,d), which should be selected according to actual needs to optimize storage and performance; 3. Constraints include NOTNULL, UNIQUE, DEFAULT, PRIMARYKEY and FOREIGNKEY. When using foreign keys, the two tables must be engines that support foreign keys (such as
    Mysql Tutorial . Database 638 2025-07-12 01:27:51
  • mysql delete from table where
    mysql delete from table where
    When deleting data using the DELETEFROMtableWHERE statement in MySQL, you must pay attention to accuracy and security. 1. This statement is used to delete records according to the specified conditions. If the WHERE condition is omitted, the entire table will be cleared; 2. Common problems include field name errors, string not quoted, improper LIKE match, etc. It is recommended to use SELECT to confirm the target data before deletion; 3. In actual operations, the principles of checking first and then deleting, adding LIMIT tests, using transaction processing, and early backup should be followed; 4. When deleting a large amount of data, it is necessary to execute it in batches to avoid table locking and performance problems. If necessary, TRUNCATE or DROP tables should be considered.
    Mysql Tutorial . Database 746 2025-07-12 01:24:51
  • mysql ifnull function
    mysql ifnull function
    IFNULL is a function in MySQL used to process NULL values. Its function is to return the first parameter when it is not NULL, otherwise it returns the second parameter. 1. Common usages include replacing the NULL value in the query results, such as "not filled in" when the phone is empty; 2. Prevent NULL from causing the entire result to be NULL in the operation, such as replacing the price of NULL with 0 and participating in multiplication calculation; 3. Use it in combination with the aggregate function to ensure that the results such as SUM are not NULL; 4. Notes include trying to keep the parameter types consistent, not be able to judge multiple NULLs, and avoiding covering up the business logic meaning; 5. It is very practical when using practical applications such as displaying user addresses or calculating employee income. Overall, IFNULL is a simple and effective
    Mysql Tutorial . Database 677 2025-07-12 01:15:31
  • how to get table size in mysql
    how to get table size in mysql
    To see how much space a table occupies in MySQL, you can achieve it in the following ways: 1. Query the size of a single table, use SQL statements to obtain the data and index size from information_schema.tables; 2. Check the size of all tables in the entire database, and list all tables through information_schema.tables and sort them by total size; 3. Use the SHOWTABLESTATUS command to quickly view the size information of the table, and pay attention to unit conversion. In addition, you should ensure access when performing these operations, and consider storage engine differences and statistical accuracy issues.
    Mysql Tutorial . Database 148 2025-07-12 00:55:10
  • mysql event scheduler example
    mysql event scheduler example
    To enable MySQL event scheduler, 1. Use SHOWVARIABLESLIKE'event_scheduler'; view the status; 2. If OFF, add event_scheduler=ON in the configuration file or run SETGLOBALevent_scheduler=ON; Create Event example: Update the "to be paid" order status for more than 30 days at 2 am every day to "cancel". The statement includes the specified name, execution frequency, start time and SQL to be executed; manage Events include SHOWEVENTS, modify ALTEREVENT, and delete DROPEVENT; Notes include permissions
    Mysql Tutorial . Database 533 2025-07-11 03:06:00
  • mysql update statement with join
    mysql update statement with join
    In MySQL, using UPDATE combined with JOIN can update data according to the association table. The syntax is: UPDATE table 1JOIN table 2ON condition SET field = value WHERE condition; common uses include: 1. Use commas to separate multiple assignment expressions when updating multiple fields; 2. Use LEFTJOIN to avoid missing main table records, and use IFNULL to process null values; 3. Use alias and add qualifiers to prevent field conflicts; precautions include: WHERE condition position affects logic, be sure to limit the update range, and it is recommended to use SELECT to verify the matching result before execution.
    Mysql Tutorial . Database 998 2025-07-11 03:02:20
  • how to check mysql version
    how to check mysql version
    To view the version of MySQL, there are several ways to do it. 1. Use the command line: Enter mysql--version or mysql-V in the terminal or CMD; 2. Execute SQL query in the MySQL client: SELECTVERSION(); or SHOWVARIABLESLIKE'version'; 3. Windows users can use command prompt or PowerShell to enter the bin folder of the MySQL installation directory to run commands; 4. Graphical tools such as MySQLWorkbench, phpMyAdmin, etc. also support viewing version information, which is suitable for users who are not familiar with the command line. Different methods apply to different scenarios:
    Mysql Tutorial . Database 818 2025-07-11 02:58:21

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