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Home

Technical Articles

Database

How to use the ROW_NUMBER function in SQL

ROW_NUMBER()assignsauniquesequentialnumbertoeachrowwithinaresultsetbasedonthespecifiedorder,anditcanalsorestartnumberingwithingroupsusingPARTITIONBY.1.Toassignsequentialnumberstoallrows,useROW_NUMBER()OVER(ORDERBYcolumn)torankrowsuniquely,evenwithdup

Sep 08, 2025 am 01:33 AM

How to create a new database in phpMyAdmin

AccessphpMyAdminbynavigatingtohttp://localhost/phpmyadminoryourhost’sprovidedURLandloginwithyourMySQLcredentials.2.Clickthe"Databases"tabinthetopmenu.3.Enteravaliddatabasenameinthe"Createdatabase"field,usingunderscoresinsteadofspa

Sep 08, 2025 am 01:04 AM

What is the information_schema database in MySQL?

information_schemaisaread-onlyvirtualdatabaseinMySQLthatprovidesmetadataaboutallotherdatabases;itcontainssystemviewslikeTABLES,COLUMNS,andSCHEMATAforqueryingdatabasestructure,enablingtaskssuchasfindingtableswithspecificcolumnsorlistingindexinformatio

Sep 08, 2025 am 12:57 AM

How to query a parent-child hierarchy in MySQL

MySQL supports querying parent-child hierarchy structures depending on the version: ① MySQL8.0 can use recursive CTE to traverse downwards (such as querying all subordinates of a manager) or trace upwards (such as the path from employees to CEO); ② Old versions need to use stored procedures to simulate recursion with temporary tables; ③ can load full data at the application layer to build a tree structure; ④ Optimization scheme includes using closure tables or path enumerations (such as storage /1/3/7/paths) to improve query performance, where path enumerations quickly obtain subtrees through LIKE matching, which is suitable for large-scale hierarchical data.

Sep 08, 2025 am 12:25 AM

How to create a stored procedure in phpMyAdmin

TocreateastoredprocedureinphpMyAdmin,selectthetargetdatabaseandclickthe"SQL"tab.2.UseDELIMITER$$tochangethedelimiter,writetheCREATEPROCEDUREstatementwithBEGINandEND,thenresetthedelimiterwithDELIMITER;.3.Executethequerybyclicking"Go&quo

Sep 08, 2025 am 12:18 AM

Is My Server Configuration Preventing Navicat from Connecting?

Yes, server configuration may block Navicat connections. 1) The server may not be configured to allow connections from your IP, or the database port is blocked by the firewall. 2) The database user may lack the necessary permissions, or the server authentication settings are incorrect. These issues can be resolved by checking network access, firewall rules, database permissions, and authentication settings.

Sep 08, 2025 am 12:08 AM

Oracle LISTAGG function example

The LISTAGG function is used to concatenate multiple rows into a single string, usually grouped by category; 1. Use LISTAGG (column, delimiter) to specify the columns and delimiters to be connected; 2. You must use WITHINGROUP (ORDERBY...) to define the connection order; 3. When aggregating by category, you need to use GROUPBY; 4. The default maximum length of the result is 4000 characters, and it is necessary to use ONOVERFLOWTRUNCATE to process; 5. You can safely truncate the extra-long string through ONOVERFLOWTRUNCATE...'WITHCOUNT and display the omitted count; this function is equivalent to MySQL's GROUP_CONCAT or

Sep 07, 2025 am 07:20 AM

oracle LISTAGG

SQL Server Transaction Log Management

The main reasons for the larger transaction log include not being regularly backed up, long-running transaction blocking and truncation, high-availability mechanism exceptions, and checkpoint not being triggered in time. 1. No log backups are done regularly, resulting in log accumulation; 2. Long-running transactions prevent log truncation; 3. Database mirroring or availability groups are not working properly; 4. Checkpoints do not trigger the cleanup of logs in time. The recovery mode should be selected according to business needs: 1. The complete mode is suitable for systems that require precise recovery, such as financial applications; 2. The simple mode is suitable for development environments and does not support point-of-time recovery; 3. The large-capacity log mode is used to reduce the log volume during large-scale operations. Log backups should be performed periodically, with reliable paths and compression enabled, while cleaning old backup files. Before shrinking the log file, you must ensure that it is truncated and frequently shrinks.

Sep 07, 2025 am 06:47 AM

How to find duplicate records in a table in Oracle

The most effective way to find duplicate records in Oracle tables is to use the GROUPBY and HAVING clauses in conjunction with the ROW_NUMBER() window function. 1. Use GROUPBY and HAVING to identify duplicate values, such as SELECTemail, COUNT()FROMemployeesGROUPBYemailHAVINGCOUNT()>1 to return duplicate email and its occurrence number; 2. To view the complete duplicate row, use ROW_NUMBER()OVER(PARTITIONBYemailORDERBYemployee_id) to assign row numbers to each group, filter rn&gt

Sep 07, 2025 am 06:42 AM

How to unpivot data in SQL?

Using the UNPIVOT operator (applicable to SQLServer and Oracle) can directly convert wide tables into long tables, with concise syntax; 2. Using UNIONALL method is suitable for all databases, merging results by column-by-column query, but the code is verbose; 3. Using LATERAL or CROSSAPPLY (PostgreSQL, SQLServer) combined with VALUES clauses, the syntax is clear and the performance is good; 4. For dynamic scenarios with unknown columns, dynamic SQL needs to be generated through system tables. The appropriate method should be selected based on the database type and column number. If UNPIVOT is supported, it will be preferred. Otherwise, LATERAL or CROSSAPPLY is recommended to ensure that the code is simple and efficient.

Sep 07, 2025 am 06:39 AM

How to bulk insert data from a CSV file in SQL

Tobulkinsertcsvdataintoasqldatabase, UnlessstheativbulkimportCommandsPecifictoyourdatabase system: Formysql, USEloadDatainfilewithp Roperfield Dandlin Terminator Sandsure File Accessibility; Outpost Greesql, Usecopyifthefileis Server-Sideor \ CopyinpsqlForClient page

Sep 07, 2025 am 06:27 AM

sql csv

SQL for Beginners: A Step-by-Step Tutorial to Writing Your First Query

Your first SQL query can start with a simple SELECT statement. 1. Use SELECT to specify the column to be retrieved, such as SELECTnameFROMemployees; 2. Use WHERE to filter the data, such as WHEREdepartment='Sales'; 3. Use ORDERBY to sort the results, such as ORDERBYsalaryDESC; 4. Use LIMIT to limit the number of rows to return, such as LIMIT5. A complete example is: SELECTname, department, salaryFROMemployeesWHEREssalary>40000ORDERBYsal

Sep 07, 2025 am 06:25 AM

How to extract the month from a date in SQL

Use the MONTH() function to extract months from dates. The specific methods vary according to the database system: 1. Use MONTH(order_date); 2. PostgreSQL, Oracle, MySQL8.0, SQLite, and BigQuery to use EXTRACT(MONTHFROMorder_date); 3. SQLServer can also use DATEPART(MONTH, order_date); 4. To get the month name, use MONTHNAME() for MySQL and TO_CHAR(order) for PostgreSQL to use TO_CHAR(order) for PostgreSQL to use DATEPART(MONTH, order_date); 4. To get the month name, use MONTHNAME() for MySQL and use TO_CHAR(order) for PostgreSQL to use DATEPART(MONTH, order_date); 4. To get the month name, use MONTHNAME() for MySQL and use TO_CHAR(order) for PostgreSQL to use TO_CHAR(order) for order.

Sep 07, 2025 am 06:19 AM

How to Use MongoDB with Node.js for a Web Application

InstallMongooseandconnecttoMongoDBusingaconnectionstring.2.Defineaschemaandmodelfordata.3.PerformCRUDoperationsinExpressroutestostore,retrieve,update,anddeletedataefficiently.

Sep 07, 2025 am 06:09 AM