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Steps to add and delete fields to MySQL tables

Steps to add and delete fields to MySQL tables

In MySQL, add fields using ALTERTABLEtable_nameADDCOLUMNnew_columnVARCHAR(255)AFTERexisting_column, delete fields using ALTERTABLEtable_nameDROPCOLUMNcolumn_to_drop. When adding fields, you need to specify a location to optimize query performance and data structure; before deleting fields, you need to confirm that the operation is irreversible; modifying table structure using online DDL, backup data, test environment, and low-load time periods is performance optimization and best practice.

Apr 29, 2025 pm 04:15 PM
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How to analyze the execution plan of MySQL query

How to analyze the execution plan of MySQL query

Use the EXPLAIN command to analyze the execution plan of MySQL queries. 1. The EXPLAIN command displays the execution plan of the query to help find performance bottlenecks. 2. The execution plan includes fields such as id, select_type, table, type, possible_keys, key, key_len, ref, rows and Extra. 3. According to the execution plan, you can optimize queries by adding indexes, avoiding full table scans, optimizing JOIN operations, and using overlay indexes.

Apr 29, 2025 pm 04:12 PM
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How to use MySQL subquery to improve query efficiency

How to use MySQL subquery to improve query efficiency

Subqueries can improve the efficiency of MySQL query. 1) Subquery simplifies complex query logic, such as filtering data and calculating aggregated values. 2) MySQL optimizer may convert subqueries to JOIN operations to improve performance. 3) Using EXISTS instead of IN can avoid multiple rows returning errors. 4) Optimization strategies include avoiding related subqueries, using EXISTS, index optimization, and avoiding subquery nesting.

Apr 29, 2025 pm 04:09 PM
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How to configure the character set and collation rules of MySQL

How to configure the character set and collation rules of MySQL

Methods for configuring character sets and collations in MySQL include: 1. Setting the character sets and collations at the server level: SETNAMES'utf8'; SETCHARACTERSETutf8; SETCOLLATION_CONNECTION='utf8_general_ci'; 2. Create a database that uses specific character sets and collations: CREATEDATABASEexample_dbCHARACTERSETutf8COLLATEutf8_general_ci; 3. Specify character sets and collations when creating a table: CREATETABLEexample_table(idINT

Apr 29, 2025 pm 04:06 PM
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How to uninstall MySQL and clean residual files

How to uninstall MySQL and clean residual files

To safely and thoroughly uninstall MySQL and clean all residual files, follow the following steps: 1. Stop MySQL service; 2. Uninstall MySQL packages; 3. Clean configuration files and data directories; 4. Verify that the uninstallation is thorough.

Apr 29, 2025 pm 04:03 PM
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How to rename a database in MySQL

How to rename a database in MySQL

Renaming a database in MySQL requires indirect methods. The steps are as follows: 1. Create a new database; 2. Use mysqldump to export the old database; 3. Import the data into the new database; 4. Delete the old database.

Apr 29, 2025 pm 04:00 PM
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How to install MySQL on Linux system

How to install MySQL on Linux system

Installing MySQL on Linux can be done through the package manager. The specific steps are as follows: 1. On Ubuntu, use apt to update the package list and install the MySQL server; 2. On CentOS, use yum to install the MySQL community version and start the service. After installation, basic configuration needs to be performed, such as setting the root password and creating database and users.

Apr 29, 2025 pm 03:57 PM
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Creation and usage scenarios of MySQL views

Creation and usage scenarios of MySQL views

MySQL views are virtual tables generated based on SQL queries. 1. Create a view: Use the CREATEVIEW statement combined with SELECT query. 2. Usage scenarios: simplify complex queries, data abstraction and ensure data consistency. 3. Optimization strategy: simplify underlying queries, use indexes, and consider materialized views.

Apr 29, 2025 pm 03:54 PM
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Specify character sets and collations when creating databases in MySQL

Specify character sets and collations when creating databases in MySQL

When creating a database in MySQL, character sets and collation rules should be specified to ensure data accuracy and improve query performance. 1) Use the CREATEDATABASEmy_databaseCHARACTERSETutf8mb4COLLATIONutf8mb4_unicode_ci command to create a database, select the utf8mb4 character set and utf8mb4_unicode_ci collation. 2) utf8mb4 supports more Unicode characters, while utf8mb4_unicode_ci provides case-insensitive comparisons. 3) Ensure that the application layer and database layer use the same character set and collation rules to avoid potential problems.

Apr 29, 2025 pm 03:51 PM
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How to sort and rank data in MySQL

How to sort and rank data in MySQL

In MySQL, sorting uses the ORDERBY clause, and ranking uses the RANK(), DENSE_RANK(), and ROW_NUMBER() functions. 1. Sort: Use ORDERBY clause, such as SELECT*FROMemployeesORDERBYsalaryDESC; 2. Ranking: Use window functions, such as SELECTemployee_name, salary, RANK()OVER(ORDERBYsalaryDESC)ASrankFROMemployees; these operations are based on SQL query optimizer and execution engine, and are often used to sort quickly or merge sort, and ranking depends on window function calculation.

Apr 29, 2025 pm 03:48 PM
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Creation and calling methods of MySQL stored procedures

Creation and calling methods of MySQL stored procedures

To create and call stored procedures in MySQL, follow the following steps: 1. Create stored procedures: Use the CREATEPROCEDURE statement to define stored procedures, including names, parameters, and SQL statements. 2. Compile stored procedures: MySQL compiles stored procedures into executable code and stores them. 3. Call stored procedure: use CALL statement and pass parameters. 4. Execute stored procedures: MySQL executes the SQL statements in it, processes parameters and returns the result.

Apr 29, 2025 pm 03:45 PM
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How to set up MySQL service automatically starts

How to set up MySQL service automatically starts

The MySQL service can be set to automatically start on Windows, Linux, and macOS. 1) On Windows, use the command "scconfigmysqlstart=auto" to configure. 2) On Linux, enable it using "sudosystemctlenablemysql". 3) On macOS, create and load the launchd configuration file to achieve automatic startup.

Apr 29, 2025 pm 03:42 PM
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How to view detailed structure information of MySQL tables

How to view detailed structure information of MySQL tables

The methods to view the MySQL table structure include: 1. Use the DESCRIBE command to view column information; 2. Use the SHOWCREATETABLE command to view table creation statements; 3. Use information_schema to query more detailed information. These methods help to quickly understand table structure and improve work efficiency.

Apr 29, 2025 pm 03:39 PM
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Detailed explanation of the installation steps of MySQL on macOS system

Detailed explanation of the installation steps of MySQL on macOS system

Installing MySQL on macOS can be achieved through the following steps: 1. Install Homebrew, using the command /bin/bash-c"$(curl-fsSLhttps://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)". 2. Update Homebrew and use brewupdate. 3. Install MySQL and use brewinstallmysql. 4. Start MySQL service and use brewservicesstartmysql. After installation, you can use mysql-u

Apr 29, 2025 pm 03:36 PM
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