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Technical Articles

Database

Building ETL Pipelines with MySQL and Other Data Sources

TobuildanETLpipelinethatpullsdatafrommultiplesources,transformsit,andloadsitintoMySQL,followthesesteps:1)Understandyourdatasources,includingMySQL(assourceortarget),APIs,CSVfiles,andotherdatabases.2)ChooseappropriatetoolslikePythonwithPandas/SQLAlchem

Sep 10, 2025 am 06:53 AM

How to use cursors in MySQL stored procedures

When using cursors, you must first declare the variable, then declare the cursor, and finally declare the processor. 1. Declare the variable and NOTFOUND processor; 2. Declare the cursor and associate the SELECT statement; 3. Open the cursor; 4. Get data in the loop and process it; 5. Close the cursor; it must be executed in this order and ensure that resources are cleaned. Cursors are only used in scenarios that must be processed line by line. Due to the low performance, set operations should be used to complete tasks first and end with a complete sentence structure.

Sep 10, 2025 am 06:52 AM

How to create a primary key in MySQL?

Defining primary keys can ensure data integrity. When creating tables, you can use PRIMARYKEY constraints to specify single column or multiple column key combinations, such as CREATETABLEusers(idINTPRIMARYKEY, nameVARCHAR(50)); for existing tables, use ALTERTABLEusersADDPRIMARYKEY(id), but the columns must be unique and non-empty; compound primary keys are suitable for multi-column combination unique scenarios, such as PRIMARYKEY(order_id, product_id); use ALTERTABLEusersDROPPRIMARYKEY to remove primary keys.

Sep 10, 2025 am 06:50 AM

mysql primary key

How to use regular expressions in MySQL with REGEXP

MySQL supports basic regular expression matching using REGEXP or RLIKE operators for performing pattern-based string searches in SQL queries. 1. You can use REGEXP to implement pattern filtering in the WHERE clause. For example, SELECTFROMusersWHEREemailREGEXP'gmail' can match the lines in which the email field contains "gmail", which is not case sensitive by default; 2. Common regular elements include. (any single character), ^ (starting of string), $ (end of string), (zero or more precedent characters), (one or more),? (zero or one), [abc] (character set), [a-z] (character specimen

Sep 10, 2025 am 06:34 AM

mysql regular expression

How to split a string into multiple columns in SQL?

TosplitastringintomultiplecolumnsinSQL,usedatabase-specificfunctions:1.InMySQL,useSUBSTRING_INDEXtoextractpartsbydelimiter;2.InPostgreSQL,useSPLIT_PARTwithpartnumberforcleanextraction;3.InSQLServer,useSTRING_SPLITwithCROSSAPPLYandpivoting,ensuringord

Sep 10, 2025 am 06:00 AM

How to calculate a year-over-year comparison in SQL?

To calculate year-on-year growth, it is recommended to use the LAG() window function or the self-connection method. 1. Use the LAG() function: summarize the data on a monthly basis through DATE_TRUNC, use LAG (monthly_revenue, 12) to obtain the revenue from 12 months ago, calculate the difference and growth rate, and use NULLIF to avoid the zero-dividing error; 2. Use self-connection: associate the current month with the same month last year through LEFTJOIN, COALESCE handles the missing values, and calculates year-on-year changes; 3. Use a complete date sequence to process missing months, pay attention to index performance and fiscalyear adjustments. The final result includes the current value, the same period last year, the difference and the growth rate, which is suitable for mainstream SQL databases.

Sep 10, 2025 am 05:35 AM

Using MongoDB as a Vector Database for AI and ML Applications

MongoDBcanstorevectorembeddingsusingarrayfields,enablingsimpleintegrationofAI/MLworkflowsintoexistingapplications.2.WithMongoDBAtlasSearch,youcanperformapproximatenearestneighbor(ANN)searchesviacosinesimilaritybycreatingavectorindexandusingthe$search

Sep 10, 2025 am 05:26 AM

How to use comments in MySQL queries?

MySQL supports a variety of comment syntax to improve the readability and maintainability of SQL code. 1. Use single-line comments - (subsequent to spaces) or #, the content from the mark to the end of the line will be ignored; 2. Use /.../ for multiple lines and can be used to comment or disable code blocks, or can be used to inline comments; 3. Use /!.../ for conditional comments, the contents will be executed by MySQL but ignored by other databases, and can also be specified versions such as /!50001.../ only in MySQL 5.0.1 and above; 4. Comments can be used to document descriptions of complex queries, temporarily disable code, debugging, or writing tutorial examples, so as to help others and future selves understand SQL logic more clearly.

Sep 10, 2025 am 05:20 AM

mysql Comment

SQL for Data Analysis: A Deep Dive into Real-World Applications

SQLfordataanalysisisessentialfortransformingrawdataintoactionableinsightsbyaskingtherightquestionsandapplyingstructuredqueryingtechniques.1.DatacleaningandpreparationinvolvehandlingNULLswithCOALESCE(),standardizingtextusingTRIM()andUPPER()/LOWER(),pa

Sep 10, 2025 am 04:49 AM

How to select rows with the MAX value for a column in SQL

To select a row with a maximum value in a certain column, the most effective way is to use a window function; for a single row of the entire table, use ROW_NUMBER()OVER(ORDERBYcolumn_nameDESC) and filter rn=1; if there is a parallel situation and all maximum rows need to be returned, use RANK(); in grouping scenarios, use PARTITIONBY combined with RANK() or ROW_NUMBER() to obtain the row corresponding to the maximum value in each group; for old databases that do not support window functions, you can query SELECT*FROMyour_tablet1WHEREcolumn_name=(SELECTMAX(colu

Sep 10, 2025 am 04:47 AM

How to use linked servers to query remote data in SQL?

AlinkedserverinSQLServerenablesqueryingremotedatasourceslikeSQLServer,Oracle,orExcelusingdistributedqueries.2.Tocreatealinkedserver,useT-SQLcommandssuchassp_addlinkedserverandsp_addlinkedsrvlogin,specifyingtheremoteservername,product,andauthenticatio

Sep 10, 2025 am 04:28 AM

How to find the Nth highest value in a table in MySQL

To find the N-highest value in the table, it is recommended to use the DENSE_RANK() function, 1. Use LIMIT and OFFSET: suitable for scenarios without duplicates or small datasets, the syntax is SELECTDISTINCT column name FROM table name ORDERBY column name DESCLIMIT1OFFSETN-1; 2. Use DENSE_RANK(): suitable for processing duplicate values ??to ensure that there is no gap in ranking, the syntax is SELECT column name FROM (SELECT column name, DENSE_RANK() OVER (ORDERBY column name DESC) ASrnkFROM table name) tWHERErnk=N; 3. Use subquery: suitable for MySQL8.0 below

Sep 10, 2025 am 04:18 AM

How to analyze Redis memory usage with the MEMORY USAGE command?

TheRedisMEMORYUSAGEcommandestimatesthememoryconsumptionofaspecifickey.1.Itaccountsforboththevalueandinternalmetadata,providingresultsinbytes.2.Youcanuseittoidentifymemory-heavykeys,comparedatastructureefficiency,ortroubleshoothighmemoryusage.3.Forlar

Sep 10, 2025 am 04:08 AM

Redis內(nèi)存

How to drop a database in MySQL?

UseDROPDATABASEdatabase_nametodeleteadatabaseinMySQL;thispermanentlyremovesthedatabaseandallitscontents.UseDROPDATABASEIFEXISTSdatabase_nametoavoiderrorsifthedatabasedoesnotexist.ThisactionisirreversibleandrequiresDROPprivileges.Alwaysverifythedataba

Sep 10, 2025 am 03:41 AM

mysql database