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Technical Articles

Database

How to Troubleshoot Common MySQL Connection Errors?

Check whether the MySQL service is running, use sudosystemctlstatusmysql to confirm and start; 2. Make sure that bind-address is set to 0.0.0.0 to allow remote connections and restart the service; 3. Verify whether the 3306 port is open, check and configure the firewall rules to allow the port; 4. For the "Accessdenied" error, you need to check the user name, password and host name, and then log in to MySQL and query the mysql.user table to confirm permissions. If necessary, create or update the user and authorize it, such as using 'your_user'@'%'; 5. If authentication is lost due to caching_sha2_password

Aug 08, 2025 am 06:44 AM

mysql connection error

How to Think in SQL: A Mental Model for Beginners

Thinkinsets,notsteps—SQLoperatesonentiredatasetsatonce,sodescribethedesiredoutcomeratherthanprocedurallogic.2.Treattablesascollectionsoffactsthatcanbefiltered,shaped,grouped,andcombinedusingWHERE,SELECT,GROUPBY,andJOIN.3.UnderstandJOINsasmatchingrows

Aug 08, 2025 am 06:38 AM

How to get the last inserted ID in MySQL

To get the last inserted ID in MySQL, use the LAST_INSERT_ID() function. 1. After executing the INSERT statement, you can directly call SELECTLAST_INSERT_ID() to get the last self-increment ID in the current session; 2. This function is session-safe and will not interfere with each other when multiple users concurrent operations; 3. Its value persists in the same connection until the next time the self-increment data is inserted; 4. Returns the valid ID only when inserting the table containing the AUTO_INCREMENT column, otherwise it will return 0; 5. In PHP, you can use the lastInsertId() method of PDO and cursor.lastro in Python.

Aug 08, 2025 am 06:26 AM

How can you upgrade a MongoDB replica set or sharded cluster with minimal downtime?

Upgrading a MongoDB replica set or sharded cluster without causing significant downtime is feasible, but best practices are required. First check version compatibility to ensure that the new version is compatible with the current settings, especially when crossing multiple major versions, you need to check the changes in the release notes and upgrade the components in sequence; secondly, use rolling upgrades for the replica set, upgrade the secondary nodes one by one, and then upgrade the main nodes, maintain at least three nodes to maintain arbitration; again upgrade the shard cluster in stages, first upgrade the configuration server, then upgrade the mongos router, and finally upgrade each shard one by one; finally, in a production-like test environment, comprehensively verify the upgrade path, including backup recovery, load performance and monitoring tool compatibility, to ensure that all steps are executed in sequence and verified correctly before going online.

Aug 08, 2025 am 06:24 AM

最小停機(jī)時(shí)間

How to view query execution time?

To view the execution time of an SQL query, it can be achieved through the database's own commands, client tools, or application-layer records. 1. Use EXPLAINANALYZE to view the actual execution time of the query in PostgreSQL or MySQL8.0. 2. SHOWPROFILE can be used in the old version of MySQL to analyze each stage time. 3. Most client tools such as DBeaver, MySQLWorkbench and psql display execution time by default. 4. The application layer can also count the query time by recording the start and end timestamps, which is suitable for code debugging and remote call scenarios.

Aug 08, 2025 am 06:05 AM

sql Performance analysis

How to find the size of a database and its tables in SQL?

To view the size of the database and its tables, you need to use the corresponding methods according to different database management systems: 1. In MySQL, query information_schema.TABLES, use data_length and index_length fields to calculate the size; 2. In PostgreSQL, use functions such as pg_database_size() and pg_total_relation_size() to format the output together with pg_size_pretty(); 3. In SQLServer, you can execute sp_spaceused stored procedures or query sys.master_files and sys.all

Aug 08, 2025 am 05:57 AM

How to copy a table to another database in MySQL

Tocopybothstructureanddata,useCREATETABLE...LIKEfollowedbyINSERTINTO...SELECT,whichpreservesindexes,constraints,andAUTO_INCREMENTsettings.2.Tocopyonlythestructure,useCREATETABLE...LIKE,whichcreatesanemptytablewiththesameschema.3.Tocopystructureanddat

Aug 08, 2025 am 05:21 AM

How to prevent SQL injection in MySQL

Usepreparedstatementswithparameterizedqueriestotreatuserinputasdata,notexecutablecode.2.Validateandsanitizeinputbyfilteringdatatypes,limitinglength,andwhitelistingvalues.3.Escapeinputsonlyifpreparedstatementsarenotfeasible,usingfunctionslikereal_esca

Aug 08, 2025 am 05:09 AM

mysql sql injection

phpMyAdmin execute bulk queries

Yes, phpMyAdmin supports batch execution of SQL queries. You only need to enter multiple semicolon-separated statements in the SQL tab and click "Go" to execute; 1. After entering the target database or table, click the "SQL" tab; 2. Enter multiple SQL statements, each ending in a semicolon; 3. Click "Go" to execute in order; but note that there may be max_allowed_packet and execution time limits. It is recommended to use the "Import" tab to upload .sql files for large files; ensure the syntax is correct and avoid partial execution due to single errors; it is recommended to wrap related operations with STARTTRANSACTION and COMMIT to ensure data consistency; use multi-line INS

Aug 08, 2025 am 05:02 AM

How to use GROUP_CONCAT in MySQL

GROUP_CONCAT is a function in MySQL that group multiple rows of data into strings by specified columns. 1. Basic splicing can be achieved through SELECTGROUP_CONCAT (column_name)FROMtable_nameGROUPBYgrouping_column; 2. Use SEPARATOR custom separators such as '|' or null values; 3. Use ORDERBYproductASC to sort the splicing contents within the function; 4. Use IFNULL or COALESCE to process NULL values; 5. Use SETSESSION or GLOBALgroup_concat_max_len

Aug 08, 2025 am 04:44 AM

mysql

How to benchmark Redis performance using redis-benchmark?

Redis's performance benchmark can be implemented through the official tool redis-benchmark. 1. Basic use: Run redis-benchmark-h127.0.0.1-p6379 to quickly test the default scenario; 2. Custom testing: Use -t to specify the command, -n to set the number of requests, and -c to set the concurrent number to simulate real load; 3. Fine control: Use -d to adjust the data size, and -P to enable pipeline batch sending commands to improve throughput; 4. Remote testing and analysis: Specify the remote IP and port, pay attention to the number of requests per second and delay distribution to evaluate performance.

Aug 08, 2025 am 04:29 AM

redis Performance Testing

How to save table filters and sort order?

In Excel and GoogleSheets, filters are not saved by default, but sorting is done. The filter status is not retained after closing the file in Excel, but the color change of the table head arrow indicates that the filter has been set and can be saved through VBA macros; the filter of GoogleSheets will be retained, but the filter status will still not be saved. Exporting filter results can be used as an alternative. Sort directly changes the data order and keep it permanently. Save it and take effect. However, it is necessary to note that merging cells and blank rows affect the accuracy of sorting, and avoid confusion caused by only sorting visible areas in the filter state.

Aug 08, 2025 am 04:15 AM

Implementing MySQL Database Patch Management

There are three reasons why patch management cannot be ignored: First, MySQL version is updated frequently, and patches are mostly used to repair security vulnerabilities or known problems; second, failure to upgrade in time may cause the database to face the risk of attack or run abnormalities, such as master-slave replication failure; third, even if you use MySQL instances on the cloud, you still need to grasp the upgrade timing and scope of impact. Three key points should be considered when judging whether to patch: whether security vulnerabilities are involved need to be handled first; whether they affect current business functions; and whether they are major changes need to be carefully evaluated. Patch testing needs to be carried out in steps: build a test environment that is consistent with the production environment, back up data in advance, perform core SQL and stress tests, check logs and application layer compatibility. Suggestions for patch release: Choose business launch during the peak period and upgrade the slave first under the master-slave architecture

Aug 08, 2025 am 04:03 AM

mysql database

How to find the DDL of a table in Oracle

To obtain the DDL of Oracle table, you should use the DBMS_METADATA.GET_DDL function, 1. Use SELECTDBMS_METADATA.GET_DDL('TABLE','Table name','Schema name')FROMDUAL; query the complete creation statement, 2. Make sure the table name and schema name are uppercase unless the original object uses double quotes to define the case, 3. Make sure the user has permission to access the data dictionary and execute DBMS_METADATA, 4. Set SETLONG20000; SETPAGESIZE0; in tools such as SQL*Plus to avoid output truncation, 5. If you only need column information, you can query USER

Aug 08, 2025 am 03:47 AM