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Technical Articles

Database

How to perform date arithmetic in MySQL

MySQL supports date operation through built-in functions and operators. 1. Use DATE_ADD() and DATE_SUB() to increase and decrease dates according to specified units (such as DAY, MONTH, etc.); 2. Use INTERVAL and -INTERVAL to simplify syntax to implement date addition and subtraction; 3. Use DATEDIFF() to calculate the difference in the number of days during the two-day period, or use TIMESTAMPDIFF() to obtain more accurate time unit differences (such as hours and minutes); 4. Common application scenarios include querying orders for the last 7 days, calculating the expiration date and user age, and ensuring that the date field type is correct and avoiding invalid date input, and finally, various date operation needs are efficiently handled through these functions and operators.

Sep 16, 2025 am 02:29 AM

How to generate a random number in Oracle?

Oracle's DBMS_RANDOM.VALUE function is used to generate random numbers, which can return floating point numbers between 0 and 1 or values ??within a specified range. For example, SELECTDBMS_RANDOM.VALUE(1,100) generates random numbers between 1 and 100; random integers can be obtained through functions such as ROUND, FLOOR, etc.; supports manual set of seeds to achieve repeatable results, which is suitable for testing scenarios.

Sep 16, 2025 am 02:22 AM

oracle random number

How to compare a column to multiple values in SQL?

Use the IN operator to efficiently compare columns with multiple values, such as SELECT*FROMemployeesWHEREdepartment_idIN(1,2,3); use NOTIN if multiple values ??are excluded, but pay attention to NULL affecting the result.

Sep 16, 2025 am 02:12 AM

sql 比較列

phpMyAdmin add user with limited privileges

LogintophpMyAdminwithadminrights;2.NavigatetoUseraccountsandclickAdduseraccount;3.Enterusername,sethost(preferablylocalhost),anduseastrongpassword;4.UnderDatabase-specificprivileges,selectthetargetdatabaseandgrantonlynecessarypermissionslikeSELECT,IN

Sep 16, 2025 am 01:52 AM

How to select distinct values in MySQL?

Use the DISTINCT keyword to remove duplicate values ??from the specified column and return unique values. 1. The basic syntax is SELECTDISTINCTcolumn_nameFROMtable_name; 2. Query the unique value of a single column, such as SELECTDISTINCTcityFROMcustomers; 3. Query the unique combination of multiple columns, such as SELECTDISTINCTcity, stateFROMcustomers; 4. Filter with the WHERE clause and get the unique value, such as SELECTDISTINCTproduct_nameFROMordersWHEREorder_date>'202

Sep 16, 2025 am 12:52 AM

mysql distinct

How to use dynamic SQL

DynamicSQLallowsbuildingandexecutingSQLstatementsatruntime,whichisessentialwhenquerycomponentsliketablenamesorconditionsareunknownuntilexecution;itiscommonlyusedinstoredproceduresforflexiblequeries,optionalfilters,DDLstatements,anddynamicordering;inS

Sep 16, 2025 am 12:51 AM

sql 動態(tài) SQL

How to use Redis as a cache with Node.js?

InstallRedisclientlikeioredisorredisvianpm,thenconnecttoRedisinNode.js.2.BeforequeryingdatabaseorAPI,checkifdataexistsinRedisusingget;iffound,returncacheddata.3.Ifnotincache,fetchfromdatabase,storeinRediswithsetExforexpiration,thenreturn.4.Ondataupda

Sep 16, 2025 am 12:34 AM

redis node.js

How to use a temporary table in MySQL?

The MySQL temporary table only exists in the current session and is used to store intermediate results for complex queries. Created with CREATETEMPORARYTABLE, such as: CREATETEMPORARYTABLEtemp_sales(idINTPRIMARYKEY,product_nameVARCHAR(100),amountDECIMAL(10,2),sale_dateDATE); this table is only visible to the current connection, and other connections cannot access the temporary table of the same name. Operations such as INSERT, SELECT, etc., such as querying records with an amount greater than 100 after inserting data. Available through DROPTEMPORARYTABL

Sep 15, 2025 am 05:25 AM

How to use window functions in MySQL?

WindowfunctionsinMySQLenablecalculationsoverasetofrowsrelatedtothecurrentrowwithoutcollapsingthem,supportingranking,runningtotals,andmore.TheyrequireMySQL8.0 .Thesyntaxis:SELECTcolumn,window_function()OVER(window_definition)FROMtable.Keyfunctionsincl

Sep 15, 2025 am 04:52 AM

How to use the IF() function in MySQL?

The answer is that MySQL's IF() function is used to execute conditional logic in SQL queries, and the syntax is IF(condition, value_if_true, value_if_false); it returns the corresponding value according to the conditions, and is often used to generate calculated columns in SELECT statements, such as judging whether the score passes, processing NULL value replacement, or implementing multi-level scoring through nesting to improve query flexibility.

Sep 15, 2025 am 04:39 AM

How to convert rows to columns dynamically in SQL?

The core method of dynamically converting rows to columns is to use dynamic perspective, and the specific implementation depends on the database system. 1. In SQLServer, first obtain the unique column value through QUOTENAME() and splice it into dynamic SQL, and then use PIVOT to combine sp_executesql to ensure security and flexibility; 2. In MySQL, use GROUP_CONCAT to generate a list expression containing SUM(IF()) and perform dynamic query through PREPARE statement; 3. Dynamic perspective is suitable for scenarios where column names are unknown or frequently changed, such as report generation, but should be avoided in situations where performance is sensitive or can be processed through the application layer; pay attention to column sorting and data type

Sep 15, 2025 am 04:00 AM

How to delete records from a MySQL table?

TodeleterecordsinMySQL,useDELETEFROMtable_nameWHEREcondition;alwaysspecifyaWHEREclausetoavoidunintendeddataloss,andtestwithSELECTfirst.Forallrows,DELETEremovesdatabutkeepsstructure,whileTRUNCATEisfasterandresetsauto-increment.Backupdataandusetransact

Sep 15, 2025 am 03:34 AM

How to Use Change Streams in MongoDB to React to Data Changes

ChangestreamsinMongoDBenablereal-timemonitoringofdatachangesacrosscollections,databases,ordeployments,requiringareplicasetorshardedclustertoaccesstheoplog;usethewatch()methodinNode.jstolistenforeventslikeinsert,update,ordelete,filterspecificchangesus

Sep 15, 2025 am 03:23 AM

How to Design a Multi-Tenant Architecture in MongoDB

Answer: Choosing the right multi-tenant data model is the key. Shared collections are suitable for small and medium-sized applications. Independent databases are suitable for high isolation requirements. Tenant isolation needs to be forced at the application layer, indexing is optimized to improve query efficiency, and manage differences between tenants through pattern verification to ensure a balance between security and performance.

Sep 15, 2025 am 03:20 AM