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Technical Articles

Database

Mysql Tutorial

how to call a stored procedure in mysql

The key to calling MySQL stored procedures is to clarify the stored procedure name and parameters, and use CALL statements or programming interfaces to call. 1. Use CALL statement to call directly: such as CALLget_user_info(123); when multi-parameters, you need to fill in order and pay attention to type matching; 2. Call in client tools: such as MySQLWorkbench executes CALL statement, if there is no return value, you can check data changes or log confirmation effect; 3. Process output parameters: define the results received by user variables, such as CALLget_total_orders(1,@total); SELECT@total; 4. Call from program code: such as Python using cursor.

Jul 10, 2025 am 11:33 AM

mysql create temporary table

A temporary table is a temporary table structure created in the current database connection and is automatically deleted after disconnection. It is suitable for saving intermediate results in complex queries, report generation or step-by-step calculations, improving execution efficiency. 1. The creation syntax is CREATETEMPORARYTABLEtemp_table_name(...) or quickly create based on query results; 2. When using it, you need to pay attention to only the current session is accessible, triggers and foreign keys are not supported, ordinary tables with the same name may be overwritten, and frequent and extensive use is avoided; 3. Typical scenarios include intermediate result sets, pagination summary, data statistics of multiple references, and data cleaning.

Jul 10, 2025 am 11:14 AM

mysql insert on duplicate key update

INSERT...ONDUPLICATEKEYUPDATE is a statement in MySQL that performs insertion or update operations when repeated key conflicts are handled. Its core mechanism is: if the insertion data does not violate the primary key or unique constraint, it will be inserted normally; if it conflicts, the update part will be executed. This statement is suitable for user registration, order writing and other scenarios, and can simplify logic and ensure data integrity. Key points of use include: 1. The table must define a primary key or a unique index; 2. The update of multiple fields must be separated by commas; 3. The insertion value can be referenced through the VALUES() function; 4. Support inserting multiple rows at a time, and each row independently determines whether to update. Notes include: Ensure the index is accurate to avoid misinterpretation, pay attention to lock performance under high concurrency, and use transaction control reasonably

Jul 10, 2025 am 11:11 AM

mysql error 1045 access denied for user 'root'@'localhost'

I encountered MySQL error 1045: Accessdeniedforuser'root'@'localhost', indicating that authentication failed when connecting to the database. Common reasons and solutions are as follows: 1. Check whether the user name and password are correct. It is recommended to use sudomysql-uroot to log in without password; 2. Confirm that the MySQL service has been started, and you can check and start the service through systemctl or brewservices; 3. Check the permission configuration, confirm the bind-address and skip-networking settings, and ensure that the root user is allowed to log in from the corresponding host; 4. If you forget your password, you can deactivate MySQL and

Jul 09, 2025 am 02:07 AM

mysql show grants for user

To view MySQL user permissions, use the SHOWGRANTS command, the syntax is SHOWGRANTSFOR'user'@'hostname'; for example, SHOWGRANTSFOR'test_user'@'localhost'; you can view the local connection user permissions; if the host name is not determined, you can use % wildcard instead. In the execution results, USAGE means no actual permissions, SELECT, INSERT, etc. are common operation permissions, and the content after ON indicates the scope of the permissions, such as mydb.* means all objects under the mydb database. This command is suitable for troubleshooting permission problems, permission migration and copying, and avoiding misdeletion of permissions. Notes include: The username and master must be matched accurately

Jul 09, 2025 am 01:59 AM

how to simulate full outer join in mysql

MySQL does not support FULLOUTERJOIN, and can be implemented through LEFTJOIN and RIGHTJOIN combined with UNION. 1. Use LEFTJOIN and RIGHTJOIN joint query, merge and deduplication through UNION, pay attention to the consistent order of the fields; 2. Use COALESCE to unify the primary key when processing duplicate data, which is convenient for subsequent processing; 3. For complex scenarios, temporary tables or subqueries can be used to process the left and right table data separately and then merge them to improve readability. The core is to merge left and right results and remove heavy weights.

Jul 09, 2025 am 01:56 AM

mysql too many connections error

When MySQL error occurs, the following steps can be solved through the following steps: 1. Log in to MySQL to execute SHOWSTATUSLIKE'Threads_connected' and SHOWVARIABLESLIKE'max_connections' to confirm whether the number of connections exceeds the limit; 2. Check whether there is a prompt for "Toomyconnections" in the log; 3. Temporarily increase the max_connections value and take effect by dynamically setting or modifying the configuration file; 4. Check PROCESSLIST and KILL to release idle connections; 5. Long-term optimization includes reasonably configuring the connection pool parameters,

Jul 09, 2025 am 01:55 AM

mysql self join example

SelfJoin is a technology in MySQL that connects the same table to itself through alias. It is often used to process hierarchical or parent-child relationship data. For example, in the employees table, use LEFTJOIN to associate employees with their boss information: SELECTe.nameASemployee_name,m.nameASmanager_nameFROMemployeeseLEFTJOINemployeeesmONe.manager_id=m.id; this query can obtain the name of each employee and his direct boss, which is suitable for organizational structure, recursive data and other scenarios. Pay attention to using alias, avoid circular references and optimize performance.

Jul 09, 2025 am 01:45 AM

mysql create read only user

The steps to create a read-only user are as follows: 1. Create a user with the CREATEUSER command, 2. GRANT command grant SELECT permissions, 3. Specify the accessed database and tables, 4. Perform FLUSHPRIVILEGES to ensure that the permissions take effect; to improve security, you can restrict visible fields through view or combine the application layer desensitization process; common problems need to be avoided such as mis-granting other permissions, not recycling of unnecessary permissions, not refreshing permissions, and improper host settings. It is recommended to check the user permissions after operation to ensure the configuration is correct.

Jul 09, 2025 am 01:44 AM

Defining Effective Primary Keys in MySQL Tables

The primary key is a field or combination that uniquely identifies records in a database table. Four principles must be followed when selecting: 1. Priority is given to using self-incremental integers such as INT or BIGINT to improve efficiency; 2. Avoid long strings such as UUID or mailboxes to avoid affecting performance; 3. Use business fields with caution, such as ID number due to poor stability; 4. Try not to use composite primary keys to maintain due to their complexity. At the same time, pay attention to the self-value-added configuration, delete the ID and do not recycle it, and do not manually insert the self-added field.

Jul 09, 2025 am 01:41 AM

mysql primary key

How to Install MySQL Server on Linux

The steps to install MySQL server on Linux include confirming the system environment, selecting the installation source, executing installation commands, and initializing settings. First, update the system software package, Ubuntu uses aptupdate&&aptgrade, and CentOS uses yumupdate; secondly, add official source options, Ubuntu downloads and installs the mysql-apt-config package and updates the source list, and CentOS installs the official rpm package; then executes the installation through aptinstallmysql-server or yuminstallmysql-server; then starts the service and sets the boot boot, and runs mysq

Jul 09, 2025 am 01:32 AM

how to connect to mysql database from python

To connect to the MySQL database, first install the pymysql library, use pip or conda to install; then establish a connection through the connect() method and create a cursor; then execute SQL statements and get the results; finally close the connection or use the context manager to automatically release the resources. Frequently asked questions include username and password errors, host IP errors, firewall restrictions, and database services not running. You can check the configuration and print exception information. It is recommended to use utf8mb4 to avoid garbled code for character sets.

Jul 09, 2025 am 01:30 AM

Optimizing complex JOIN operations in MySQL

TooptimizecomplexJOINoperationsinMySQL,followfourkeysteps:1)EnsureproperindexingonbothsidesofJOINcolumns,especiallyusingcompositeindexesformulti-columnjoinsandavoidinglargeVARCHARindexes;2)ReducedataearlybyfilteringwithWHEREclausesandlimitingselected

Jul 09, 2025 am 01:26 AM

mysql JOIN optimization

mysql error 2002 can't connect to local mysql server

The clear answer to MySQL error 2002 is that it fails to connect to the local MySQL server. The common reasons and solutions are as follows: 1. The MySQL service is not running. Check and start the service to check the logs; 2. When using localhost, go to the socket file path error, try to connect with 127.0.0.1 or specify the correct socket path; 3. Firewall or permission restrictions block the connection, check the bind-address configuration and port monitoring; 4. Database crashes or initialization fails, view the logs and repair or reinstall MySQL.

Jul 09, 2025 am 01:10 AM

mysql error Connection failed