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Technical Articles

Database

Mysql Tutorial

MySQL Triggers: Coding samples

MySQLtriggersshouldbeusedtoautomateactions,maintaindataintegrity,enforcebusinessrules,andautomateroutinetasks.1)Usetriggerstologchanges,likeupdatinganemployeelogtable.2)Implementtriggerstoenforcerules,suchaspreventingsalarydecreases.3)Usetriggerstoup

Jun 05, 2025 am 12:05 AM

The function of having in mysql filters grouping results

The HAVING clause is used in MySQL to filter the results after grouping. 1) HAVING is used to filter the aggregate function results after grouping, such as filtering salespeople with sales of more than 1,000. 2) When using it, you should be careful that it may cause a degradation in query performance and can only be used for queries containing GROUPBY. 3) Optimization suggestions include filtering data as early as possible in the WHERE clause, simplifying expressions in HAVING and using indexes.

Jun 04, 2025 pm 06:39 PM

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How to adjust mysql into Chinese interface? Easy to set the Chinese language environment of mysql

To tune MySQL into a Chinese interface, it can be implemented through MySQLWorkbench or command line tools. 1) In MySQLWorkbench, open "Preferences", select the "Appearance" tab, and then select "Chinese(Simplified)" in the "Language" drop-down menu, and restart. 2) When using command line tools, set the operating system locale variables, such as using "exportLANG=zh_CN.UTF-8" on Linux or macOS, and then run the mysql client.

Jun 04, 2025 pm 06:36 PM

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Where is the primary and foreign key compound key in mysql?

Primary keys, foreign keys, and compound keys are usually created in MySQL in CREATETABLE statements. 1. The primary key can be added to the PRIMARYKEY keyword after the field definition or the table definition at the end. 2. Use the FOREIGNKEY keyword at the end of the table definition, and make sure that the reference table and fields already exist. 3. Compound keys and multi-field keys are also defined in CREATETABLE. The impact of field order on query performance needs to be considered. Multi-field keys are useful in complex queries but will increase the index size.

Jun 04, 2025 pm 06:33 PM

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How to implement data sharding in mysql? Sharding optimization method

MySQL itself does not have built-in data sharding function, but can be implemented through architectural design and tools. Data sharding is to split large table data into multiple databases or tables according to rules to improve performance. Common implementation methods include: 1. Hashing fragments by user ID, which are evenly distributed but troublesome to expand capacity; 2. Shaving fragments by range, which are suitable for time-class fields but are easy to hot spots; 3. Consistent hashing algorithms, which reduce the amount of expansion migration but complex implementation. After sharding, cross-slice query, data migration, distributed transactions and other problems need to be dealt with. Middleware such as MyCat, Vitess or application layer logic processing can be used, and shard keys should be selected reasonably, shard balance should be monitored, excessive sharding should be avoided, and backup strategies should be improved.

Jun 04, 2025 pm 06:30 PM

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How to enter mysql database. Three detailed steps for login methods

There are three ways to enter the MySQL database: 1. Log in through the command line, enter "mysql-u username-p" and enter the password as prompted; 2. Use MySQLWorkbench to create a new connection and enter relevant information; 3. Log in through the Python programming language, and use the mysql.connector library to connect to the database.

Jun 04, 2025 pm 06:27 PM

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How to optimize mysql query performance? How to use mysql index?

Optimizing MySQL query performance and correct use of indexes must start from four aspects: reasonable index creation, avoiding full table scanning, optimizing SQL writing, and regular table maintenance. 1. Create index reasonably, the primary key will automatically have an index. Fields commonly used for query conditions such as user ID and order number are recommended to add indexes. When combined queries are often used, joint indexes can be used and the leftmost matching principle is adhered to; 2. Avoid full table scanning, check whether to use indexes through EXPLAIN, and avoid index failure due to function operations, fuzzy query start with wildcards, type conversion, and OR connections; 3. Optimize SQL writing, avoid SELECT*, reduce data transmission, and use JOIN instead of multi-layer subqueries, and use index-based cursors when paging big data; 4. Regularly analyze and maintain tables, use

Jun 04, 2025 pm 06:24 PM

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How to optimize mysql memory? What are the key parameters?

The core of MySQL memory optimization is to rationally configure key parameters to improve performance. 1. Adjust innodb_buffer_pool_size to 50%~80% of physical memory. For example, the 32GB server can be set to 24GB, and combine multiple instances to reduce contention. 2. Control the connection memory. The thread_stack is recommended to not be less than 192KB. The sort_buffer_size is set to 1MB~2MB to avoid memory waste. 3. Configure the global memory parameters tmp_table_size and max_heap_table_size to 128M to avoid temporary table drops. 4. Maintain the monitoring tool through SHOWENGINEINNODBSTATUS and monitoring tools

Jun 04, 2025 pm 06:21 PM

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What is mysql transaction? How to ensure data consistency?

The ACID characteristics of a transaction refer to atomicity, consistency, isolation and persistence. Atomicity ensures that all operations in a transaction are done or not; consistency ensures that the database is transferred from one consistent state to another; isolation prevents mutual interference when multiple transactions are executed concurrently; persistence ensures that the results of the transaction are permanently saved after the transaction is committed. Transactions ensure data consistency through redolog, undolog and lock mechanisms. RedoLog is used for crash recovery, UndoLog supports rollback and MVCC, and the lock mechanism controls concurrent access to avoid dirty reading, non-repeatable reading and phantom reading. Correct use of transactions requires reasonable control of transaction boundaries and the appropriate isolation level is selected. For example, READCOMMITTED is suitable for most scenarios, REPEA

Jun 04, 2025 pm 06:18 PM

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What are the mysql data types? How to choose the right type?

Choosing the right MySQL data type can save storage space, improve query performance and ensure data accuracy. Common data types are divided into numerical types (such as INT, DECIMAL), string types (such as CHAR, VARCHAR), and date and time types (such as DATE, DATETIME, TIMESTAMP). Several key points should be followed when choosing: 1. Save storage space, such as TINYINT in the status field; 2. Improve query efficiency, give priority to the use of fixed-length types; 3. Avoid accuracy loss, use DECIMAL in the amount field; 4. Pay attention to the difference in default behavior, such as TIMESTAMP automatically handles time zones. Common scenario recommendations: Use INTUNSIGNED or BIGINT for user ID,

Jun 04, 2025 pm 06:15 PM

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Command to create a table in mysql Detailed explanation of the new data table command

Create tables in MySQL using the CREATETABLE command. The specific steps include: 1) Defining the table name and column, such as CREATETABLEusers(idINTAUTO_INCREMENTPRIMARYKEY,usernameVARCHAR(50)NOTNULLUNIQUE,emailVARCHAR(100)NOTNULLUNIQUE,passwordVARCHAR(255)NOTNULL,created_atTIMESTAMPDEFAULTCURRENT_TIMESTAMP); 2) Add constraints, such as FOREIGNKEY; 3)

Jun 04, 2025 pm 06:12 PM

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Resolve errors when PHP updates MySQL database data

To resolve the errors in PHP when updating MySQL database data, you can use the following steps: 1. Check for SQL syntax errors and ensure that the table name, field name and WHERE conditions are correct. 2. Verify the database connection configuration to ensure that the user name and password are correct. 3. Confirm that the database user has sufficient permissions. 4. Use preprocessing statements to prevent SQL injection and reduce syntax errors. 5. Application transactions ensure data consistency. 6. Improve the error handling mechanism to avoid program crashes. 7. Regularly update the database configuration. 8. Consider using ORM tools to simplify code and reduce errors.

Jun 04, 2025 pm 06:09 PM

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MySQL command line operation list Complete guide to using terminal mode

Using the MySQL database in terminal mode can be performed through the following steps: 1. Connect to the MySQL server and use the command mysql-uusername-p. 2. Create databases and tables, using the CREATEDATABASE and CREATETABLE commands. 3. Execute the SQL script and import the script using the source command. 4. Query the data and use DESCRIBE or SHOWCREATETABLE to view the table structure. 5. Optimize queries and use EXPLAIN to analyze the execution plan. 6. Process large-scale data, using LIMIT and OFFSET to process it in batches. Through these steps, the database can be managed and operated efficiently.

Jun 04, 2025 pm 06:06 PM

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A complete list of commonly used commands for mysql databases 30 most commonly used commands for administrators

MySQL administrators should master 30 key commands: 1. SHOWDATABASES view all databases; 2. USE SHOWTABLES view tables in the database; 3. DESCRIBE view table structure; 4. INSERT/UPDATE/DELETE operation data; 5. SELECT query data; 6. mysqldump backup and recovery database; 7. EXPLAIN analysis query execution plan; 8. CREATEUSER/GRANT/REVOKE/DROPUSER manage users and permissions; 9. SHOWPROCESSLIST/SHOWENGINE/CHECK/REPAIR/OPTIM

Jun 04, 2025 pm 06:03 PM

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