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Home

Technical Articles

Database

Mysql Tutorial

How to describe a table in MySQL

To describe the MySQL table structure, you can use the DESCRIBE or DESC commands; 1. Use DESCRIBEtable_name or DESCtable_name to view the field name, data type, whether NULL, key type, default value and extra attributes are allowed; 2. Use SHOWCREATETABLEtable_name to obtain complete table building statements containing primary keys, unique keys, storage engines and character sets; 3. Query the INFORMATION_SCHEMA.COLUMNS table to obtain detailed metadata such as column annotations, permissions, etc., and select the appropriate method according to your needs to complete a comprehensive understanding of the table structure.

Aug 11, 2025 pm 07:05 PM

How to revoke privileges from a user in MySQL

TorevokeprivilegesfromauserinMySQL,usetheREVOKEstatement;1.Specifytheprivilegetype(e.g.,SELECT,INSERT,ALLPRIVILEGES);2.Definethescopeusingdatabase_name.table_name(e.g.,mydb.usersormydb.*);3.Identifytheexact'username'@'host'account;4.OptionallyrevokeG

Aug 11, 2025 pm 06:34 PM

What is the character set and collation in MySQL?

Acharactersetdefineswhichcharacterscanbestored,whileacollationdetermineshowtheyarecomparedandsorted.1.Charactersetslikeutf8mb4supportfullUnicode,includingemojisandinternationalcharacters.2.Collationssuchasutf8mb4_0900_ai_ciproviderulesforcase-insensi

Aug 11, 2025 pm 05:22 PM

mysql character set

How to migrate from SQL Server to MySQL

First, clear the answer: Migrating from SQLServer to MySQL requires evaluation, transformation, migration, testing and adjustment in steps. 1. Evaluate the source database, inventory the objects and identify dependency and incompatibility characteristics; 2. Map the data type differences, such as INTIDENTITY to INTAUTO_INCREMENT, NVARCHAR to VARCHAR and set the utf8mb4 character set, DATETIME maintains the corresponding, BIT to TINYINT(1), UNIQUEIDENTIFIER to CHAR(36) or BINARY(16); 3. Through the MySQLWorkbench migration wizard, manual export import or third-party tools such as AWSDMS

Aug 11, 2025 pm 04:09 PM

How to use the WHERE clause in MySQL

TheWHEREclauseinMySQLfiltersrecordsbasedonspecifiedconditions.1.ItisusedinSELECT,UPDATE,andDELETEstatementstoaffectonlymatchingrows.2.Comparisonoperatorslike=,!=,,=allowprecisefiltering.3.LogicaloperatorsAND,OR,andNOTcombinemultipleconditions,requiri

Aug 11, 2025 pm 03:54 PM

Implementing Row-Level Security in MySQL

MySQLdoesnothavebuilt-inrow-levelsecurity,butitcanbeimplementedusingviews,storedprocedures,andaccesscontrol.1.UseviewstofilterrowsbasedonthecurrentuserbyleveragingfunctionslikeCURRENT_USER()andamappingtabletorestrictdatavisibility.2.Restrictdirecttab

Aug 11, 2025 pm 01:33 PM

How to compare two tables for differences in MySQL

To compare the differences between two tables in MySQL, different operations need to be performed according to the structure, data or both: 1. When comparing the table structure, use DESCRIBE or query INFORMATION_SCHEMA.COLUMNS to find columns that exist only in one table through UNIONALL and subqueries; 2. When comparing table data, use LEFTJOIN combined with ISNULL conditions to find rows that exist only in table1 or table2, and use UNIONALL to merge the results with UNIONALL; 3. When comparing rows with the same primary key but different data, use JOIN to connect the two tables and use NULL safe comparison operator to detect the difference in the values of each column; 4. You can first perform row count statistics checks and compare them through COUNT(*)

Aug 11, 2025 pm 12:14 PM

Optimizing MySQL for High-Throughput Message Queues

TouseMySQLefficientlyasamessagequeueunderhigh-throughputworkloads,followthesesteps:1)UseInnoDBwithproperindexing—createcompositeindexesonselectivefieldslikequeue_nameandstatus,avoidexcessiveindexestomaintaininsertperformance.2)Usebatchoperations—inse

Aug 11, 2025 am 11:26 AM

How to back up a database in MySQL

Using mysqldump is the most common and effective way to back up MySQL databases. It can generate SQL scripts containing table structure and data. 1. The basic syntax is: mysqldump-u[user name]-p[database name]>backup_file.sql. After execution, enter the password to generate a backup file. 2. Back up multiple databases with --databases option: mysqldump-uroot-p--databasesdb1db2>multiple_dbs_backup.sql. 3. Back up all databases with --all-databases: mysqldump-uroot-p

Aug 11, 2025 am 10:40 AM

mysql database backup

How to use CASE statements in MySQL

SearchedCASEisusedforcomplexconditionswithexplicitcomparisonslike>,

Aug 11, 2025 am 10:29 AM

How to perform a case-insensitive search in MySQL?

MySQL is case-insensitive by default. Usually, _ci collation is used to achieve case-insensitive search; 1. Use the default case-insensitive collation (such as utf8mb4_general_ci) to make equal value comparisons and LIKE automatically ignore case; 2. Use LOWER() or UPPER() functions to convert the comparison to the same case to the same case, but be careful to affect the index usage; 3. Use COLLATE to specify temporary case-insensitive collation to overwrite the original settings of the column; 4. MySQL does not support the ILIKE operator, and LIKE combined with LOWER() or COLLATE to achieve similar functions; the best practice is to ensure that the column uses _ci collation

Aug 11, 2025 am 09:47 AM

mysql 大小寫不敏感搜索

How to schedule events in MySQL to run at specific times?

To use the MySQL event scheduler to schedule events at a specific time, you must first enable the event scheduler, then create one-time or periodic events, and finally manage the events through relevant commands; the specific steps are: 1. Execute SETGLOBALevent_scheduler=ON to enable the event scheduling function; 2. Use CREATEEVENT to specify the specific time to perform SQL operations, such as DELETEFROMlogsWHEREcreated_at

Aug 08, 2025 pm 05:43 PM

scheduled tasks

How to delete rows from a table with a self-referencing foreign key

To safely delete rows in a table with self-referenced foreign keys, the dependency must be processed first. The following three methods can be adopted: 1. If the table structure can be modified, use ONDELETECASCADE to automatically delete all child rows when deleting the parent row, but be careful to prevent accidental deletion of large amounts of data; 2. Manually control the deletion order, first delete the leaf nodes through recursive CTE, and gradually delete upwards, for example, use the WITHRECURSIVE clause to locate the specified node and all subordinates and delete them in batches; 3. Only temporarily disable foreign key checking (SETFOREIGN_KEY_CHECKS=0) in a controlled environment, and re-enable it after operation, but this method has high risk, which may lead to inconsistent data. Best practice is to combine recursive CTE with precise deletion

Aug 08, 2025 pm 05:40 PM

How to execute a query in Python using MySQL Connector

To use MySQLConnector to execute queries in Python, you first need to install and import the mysql-connector-python library, then establish a database connection, then create a cursor object to execute SQL statements, obtain the results or submit transactions according to the query type, and finally close the cursor and connection. 1. Install the library: pipinstallmysql-connector-python; 2. Import the library: importmysql.connector; 3. Establish the connection: conn=mysql.connector.connect(host='localhost',user='your_usern

Aug 08, 2025 pm 05:39 PM