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Home

Technical Articles

Database

Mysql Tutorial

How to create a temporary table in MySQL

To create a MySQL temporary table, use the CREATETEMPORARYTABLE statement; 1. The temporary table is only visible in the current session and automatically deletes when the session ends; 2. It can have the same name as the permanent table, and the temporary table is preferred within the session; 3. Use standard statements such as INSERT and SELECT to operate the data; 4. The temporary table can be manually deleted through DROPTEMPORARYTABLE to avoid accidentally deleting permanent tables.

Sep 09, 2025 am 05:06 AM

How to use prepared statements in MySQL?

The use of preprocessing statements can effectively prevent SQL injection and improve the performance of multiple queries. It is separated from the SQL structure and data, first implemented using PREPARE, SET, EXECUTE and DEALLOCATE commands in MySQL, or implemented in programming languages ??such as PHP, Python, Java, etc. through preprocessing mechanisms supported by drivers such as PDO, mysql-connector-python, JDBC. The placeholder (? or named parameters) can only represent values ??and cannot be used for table names, column names or SQL keywords. In the IN clause, placeholders need to be set separately for each value. This method has the advantages of high security, excellent performance and clear code, and has become the best database operation.

Sep 09, 2025 am 04:57 AM

How to handle character encoding issues like UTF8 in MySQL?

The utf8mb4 character set must be used to ensure that MySQL correctly handles UTF-8 encoding, including emoji and multilingual characters, because MySQL's utf8 is a pseudo-UTF-8, which only supports up to 3 byte characters and cannot store 4 byte characters; while utf8mb4 supports complete UTF-8 encoding, so CHARACTERSETutf8mb4COLLATEutf8mb4_unicode_ci should be explicitly set at the database, table, and column levels to obtain accurate sorting and comparison capabilities; at the same time, the default character set of client, mysql and mysqld parts must be set to utf8mb4 in the MySQL configuration file, and the client character set handshake should be skipped to strengthen the

Sep 09, 2025 am 04:04 AM

mysql utf8

How to set up replication in MySQL

Configure the server-id of the master server, enable binary logs and set log format; 2. Create a dedicated user for replication and grant permissions; 3. Configure the unique server-id of the slave server; 4. Get the binary log file name and location on the master server; 5. Execute the CHANGEREPLICATIONSOURCETO command on the slave server and start replication; 6. Verify the replication status through SHOWREPLICASTATUS to ensure that the IO and SQL threads run normally and have no errors; 7. If the master library already has data, it needs to be exported using mysqldump and imported into the slave library to ensure data consistency, and finally realize master-slave data synchronization.

Sep 09, 2025 am 03:34 AM

How to optimize LIKE queries with a leading wildcard in MySQL

Use reverse index to convert suffix searches into prefix searches, thereby improving performance using indexes; 2. For word-based searches, use FULLTEXT index to achieve efficient full-text search; 3. Use generated columns to pre-calculate and index the query values ??of fixed patterns in MySQL5.7; 4. For complex partial matching or frequent search requirements, external search engines such as Elasticsearch are used; 5. Optimize queries by combining index conditions, limiting the return results, and using overlay indexes to reduce the impact of full table scanning.

Sep 09, 2025 am 03:22 AM

How to connect to a MySQL database using Java (JDBC)?

Add MySQLJDBC driver, and introduce JAR packages through Maven dependencies or manually; 2. Modern JDBC versions do not need to explicitly load the driver; 3. Use DriverManager.getConnection() method to establish a connection with the correct URL, username and password; 4. Automatically close resources and handle SQLException through try-with-resources; 5. Simple query test connections can be executed, such as SELECTNOW(); Common problems include driver not found, access denied, connection denied and time zone errors. You need to ensure that the driver is in the classpath, credentials, MySQL service is running and configured with appropriate time zone parameters. After the connection is successful, you can enter normally.

Sep 09, 2025 am 02:50 AM

How to Troubleshoot MySQL Replication Lag?

First, confirm the replication status, 1. Run SHOWSLAVESTATUS\G to check whether Slave_IO_Running and Slave_SQL_Running are Yes, whether Seconds_Behind_Master values ??are too high, and whether there is Last_Error; 2. Determine the delay type, if the IO thread is normal but the delay increases, it may be a bottleneck of SQL threads. If the IO thread stops, it may be a network or authentication problem; 3. Troubleshoot common causes and fixes, including: optimizing connection or compression protocols during network delay, upgrading hardware or adjusting InnoDB parameters during resource bottlenecks, enabling parallel replication during single-thread playback (set slave_paralle

Sep 09, 2025 am 01:24 AM

mysql Replication delay

How to implement a hierarchical data structure (tree) in MySQL

AdjacencyListModelusesparent-childreferencesandissimpletoimplementbutrequiresMySQL8 CTEsforefficienttraversal.2.PathEnumerationstoresfullpathsasstrings,enablingfastsubtreeandancestorquerieswithoutrecursion,thoughupdatesarecostly.3.NestedSetModelusesl

Sep 09, 2025 am 12:02 AM

What is the purpose of the HAVING clause in MySQL?

HAVING is used to filter grouped data after GROUPBY, especially when the conditions involve aggregation functions such as COUNT and SUM; for example, if you look for departments with more than 5 employees, you need to use HAVINGCOUNT(*)>5; unlike WHERE, WHERE filters a single row before grouping and cannot use an aggregate function, HAVING filters after grouping and supports an aggregate function; the two can be used in combination, such as first using WHERE to screen employees with a salary of more than 30,000, then group them by department, and finally use HAVING to screen departments with an average salary of more than 50,000, so as to achieve effective filtering of the aggregated data and fully support complex query needs.

Sep 08, 2025 am 04:26 AM

mysql HAVING子句

How to create an index in MySQL

Creating indexes can improve query performance. It should be created on columns frequently used in WHERE, JOIN, ORDERBY or GROUPBY; 2. Use CREATEINDEXindex_nameONtable_name(column_name) to create a single column index; 3. Use composite index for multi-column joint queries, with the syntax CREATEINDEXindex_nameONtable_name(column1,column2), note that the column order affects index usage; 4. The index can be directly defined when CREATETABLE; 5. Use CREATEUNIQUEINDEX to ensure that the column values ??are unique and prevent duplication; 6. Pass A

Sep 08, 2025 am 04:19 AM

How to add a column to a table in MySQL?

To add columns to an existing table, you need to use the ALTERTABLE statement to the ADDCOLUMN clause; for example, ALTERTABLEusersADDCOLUMNemailVARCHAR(100) can add email columns to the users table; you can add constraints such as NOTNULL and DEFAULT at the same time, such as automatically recording time when creating a time column; you can specify the location of the column through FIRST or AFTER; support adding multiple columns at a time to improve efficiency; be careful when operating large tables to avoid locking tables affecting performance, and backup data should be backed up before modification. If you add non-empty columns, the default value must be set to prevent the operation from failing.

Sep 08, 2025 am 03:23 AM

mysql database

What is a NATURAL JOIN in MySQL?

ANATURALJOINinMySQLautomaticallyjoinstablesbasedoncolumnswiththesamenameandcompatibledatatypes,returningonlyonecopyofeachcommoncolumn;itrequiresnoexplicitONorUSINGclause,makingitconcisebutriskyduetoimplicitbehaviorthatcanleadtounexpectedresultsifsche

Sep 08, 2025 am 03:04 AM

mysql join

How to use user-defined variables in MySQL

User-defined variables start with @, and are assigned through SET or :=, which are only valid in the current session. They can be used to store values, simulate line numbers, etc. 1. Set variables using SET or SELECT; 2. Reference variables in subsequent statements; 3. Pay attention to the session scope and initialization, avoid undefined use, and finally end with a complete statement.

Sep 08, 2025 am 02:19 AM

How to connect to MySQL using Node.js

Install the mysql2 package: Run npminstallmysql2 to obtain a MySQL client with better performance and support Promise; 2. Create a connection: Use the mysql.createConnection() method and pass in the correct host, user name, password and database name to establish a connection; 3. Execute query: execute SQL statements through the connection.query() method and process the results; 4. Close the connection: Call the connection.end() method to safely close the connection; 5. Use Promise: Introduce the 'mysql2/promise' module to support async/await syntax to improve the readability of asynchronous operations

Sep 08, 2025 am 02:10 AM