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Home

Technical Articles

Database

Mysql Tutorial

Building ETL Pipelines with MySQL and Other Data Sources

TobuildanETLpipelinethatpullsdatafrommultiplesources,transformsit,andloadsitintoMySQL,followthesesteps:1)Understandyourdatasources,includingMySQL(assourceortarget),APIs,CSVfiles,andotherdatabases.2)ChooseappropriatetoolslikePythonwithPandas/SQLAlchem

Sep 10, 2025 am 06:53 AM

How to use cursors in MySQL stored procedures

When using cursors, you must first declare the variable, then declare the cursor, and finally declare the processor. 1. Declare the variable and NOTFOUND processor; 2. Declare the cursor and associate the SELECT statement; 3. Open the cursor; 4. Get data in the loop and process it; 5. Close the cursor; it must be executed in this order and ensure that resources are cleaned. Cursors are only used in scenarios that must be processed line by line. Due to the low performance, set operations should be used to complete tasks first and end with a complete sentence structure.

Sep 10, 2025 am 06:52 AM

How to create a primary key in MySQL?

Defining primary keys can ensure data integrity. When creating tables, you can use PRIMARYKEY constraints to specify single column or multiple column key combinations, such as CREATETABLEusers(idINTPRIMARYKEY, nameVARCHAR(50)); for existing tables, use ALTERTABLEusersADDPRIMARYKEY(id), but the columns must be unique and non-empty; compound primary keys are suitable for multi-column combination unique scenarios, such as PRIMARYKEY(order_id, product_id); use ALTERTABLEusersDROPPRIMARYKEY to remove primary keys.

Sep 10, 2025 am 06:50 AM

mysql primary key

How to use regular expressions in MySQL with REGEXP

MySQL supports basic regular expression matching using REGEXP or RLIKE operators for performing pattern-based string searches in SQL queries. 1. You can use REGEXP to implement pattern filtering in the WHERE clause. For example, SELECTFROMusersWHEREemailREGEXP'gmail' can match the lines in which the email field contains "gmail", which is not case sensitive by default; 2. Common regular elements include. (any single character), ^ (starting of string), $ (end of string), (zero or more precedent characters), (one or more),? (zero or one), [abc] (character set), [a-z] (character specimen

Sep 10, 2025 am 06:34 AM

mysql regular expression

How to use comments in MySQL queries?

MySQL supports a variety of comment syntax to improve the readability and maintainability of SQL code. 1. Use single-line comments - (subsequent to spaces) or #, the content from the mark to the end of the line will be ignored; 2. Use /.../ for multiple lines and can be used to comment or disable code blocks, or can be used to inline comments; 3. Use /!.../ for conditional comments, the contents will be executed by MySQL but ignored by other databases, and can also be specified versions such as /!50001.../ only in MySQL 5.0.1 and above; 4. Comments can be used to document descriptions of complex queries, temporarily disable code, debugging, or writing tutorial examples, so as to help others and future selves understand SQL logic more clearly.

Sep 10, 2025 am 05:20 AM

mysql Comment

How to find the Nth highest value in a table in MySQL

To find the N-highest value in the table, it is recommended to use the DENSE_RANK() function, 1. Use LIMIT and OFFSET: suitable for scenarios without duplicates or small datasets, the syntax is SELECTDISTINCT column name FROM table name ORDERBY column name DESCLIMIT1OFFSETN-1; 2. Use DENSE_RANK(): suitable for processing duplicate values ??to ensure that there is no gap in ranking, the syntax is SELECT column name FROM (SELECT column name, DENSE_RANK() OVER (ORDERBY column name DESC) ASrnkFROM table name) tWHERErnk=N; 3. Use subquery: suitable for MySQL8.0 below

Sep 10, 2025 am 04:18 AM

How to drop a database in MySQL?

UseDROPDATABASEdatabase_nametodeleteadatabaseinMySQL;thispermanentlyremovesthedatabaseandallitscontents.UseDROPDATABASEIFEXISTSdatabase_nametoavoiderrorsifthedatabasedoesnotexist.ThisactionisirreversibleandrequiresDROPprivileges.Alwaysverifythedataba

Sep 10, 2025 am 03:41 AM

mysql database

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