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Technical Articles

Database

How to convert an integer to a string in SQL?

To convert integers into strings, you should choose the appropriate method according to the database system: 1. Use CAST() function, such as SELECTCAST(123ASVARCHAR(10)), which complies with the ANSISQL standard and is suitable for PostgreSQL, SQLServer, MySQL, Oracle and SQLite, etc., with the best cross-database compatibility; 2. Use CONVERT() function, such as SELECTCONVERT(VARCHAR(10), 123), which is mainly used for SQLServer and MySQL, supports format conversion, but the syntax varies from database to database; 3. Database-specific functions include Oracle's TO_CHA

Sep 02, 2025 am 03:02 AM

What is the SUBSTRING_INDEX() function in MySQL?

SUBSTRING_INDEX()extractsasubstringfromastringbasedonadelimiterandoccurrencecount,returningtheportionbeforethespecifiednumberofdelimiteroccurrenceswhencountispositiveandafterwhennegative,makingitidealforparsingemailaddresses,filepaths,andURLsinMySQLd

Sep 02, 2025 am 02:50 AM

mysql

How to perform an INNER JOIN in SQL

AnINNERJOINreturnsonlyrowswithmatchingvaluesinbothtables;1)UseSELECTtospecifydesiredcolumns;2)UseFROMforthefirsttable;3)UseINNERJOINwiththesecondtable;4)UseONtodefinethejoincondition,typicallymatchingprimaryandforeignkeys;5)Optionally,joinmultipletab

Sep 02, 2025 am 02:39 AM

How to increase the upload file size in phpMyAdmin

To solve the problem of phpMyAdmin failing to import large SQL files, you need to modify the upload limit parameters in the PHP configuration file php.ini. 1. Find and edit the php.ini file. The path varies according to the server environment. For example, the Ubuntu system is usually located in /etc/php/8.1/apache2/php.ini, and XAMPP under Windows is C:\xampp\php\php.ini; 2. Modify the key parameters: set upload_max_filesize to 256M, post_max_size to 300M, memory_limit to 512M, max_execution_

Sep 02, 2025 am 02:16 AM

File Upload

Redis vs Traditional DB: Best code practices

Redisisidealforspeedandreal-timedataprocessing,whiletraditionaldatabaseslikeMySQLorPostgreSQLarebetterforcomplextransactionsanddataintegrity.1)UseRedisforcaching,real-timeanalytics,andsessionmanagementwithappropriatedatastructuresandexpirationtimes.2

Sep 02, 2025 am 02:09 AM

redis database

How to connect to MySQL using PHP with PDO

Connecting MySQL to PDO using PHP is a safe and flexible method. 1. First set up a DSN containing the host, database name, user name, password and character set, and configure PDO options; 2. Key options include enabling exception mode, setting the associative array to return results, and disabling preprocessing statement simulation to improve security; 3. Use prepare and execute methods to combine placeholders to perform query or insert operations to effectively prevent SQL injection; 4. Use question marks or named parameters to bind data during query to ensure that all user input is processed through the preprocessing mechanism, thereby ensuring the security and maintainability of the application.

Sep 02, 2025 am 02:04 AM

How to Use MongoDB for Content Management Systems

MongoDBexcelsinCMSenvironmentsduetoitsflexibledocumentmodel,enablingdynamiccontentstoragelikearticles,media,anduserprofilesinJSON-likeformatwithoutfixedschemas.Itsupportsnesteddataandevolvingfields,allowingseamlessadditionofnewcontenttypes.Richqueryi

Sep 02, 2025 am 01:41 AM

cms mongodb

How to get the last day of the month in SQL

SQLServerusesEOMONTH()togetthelastdayofthemonth,suchasEOMONTH('2024-03-15')returning'2024-03-31'.MySQLandOraclebothsupporttheLAST_DAY()function,whereLAST_DAY('2024-03-15')returnsthelastdayofMarch2024.PostgreSQLlacksabuilt-infunctionbutachievestheresu

Sep 02, 2025 am 12:21 AM

sql 月末日期

What is the difference between SUNION and SUNIONSTORE?

The main difference between SUNION and SUNIONSTORE is the way of processing the result. 1.SUNION is used to return union elements of multiple collections, without modifying data, and is suitable for temporary viewing of results; 2.SUNIONSTORE stores union results in a new key, and is suitable for scenarios where persistent results are required. Both times have O(N), but SUNIONSTORE may have a greater impact on performance due to write operations. You should pay attention to memory usage and execution timing when using it.

Sep 02, 2025 am 12:12 AM

redis Set operations

How to rename a table in phpMyAdmin

To rename a table in phpMyAdmin, use the Actions tab. 1. Log in to phpMyAdmin and select the target database. 2. Click the table you want to rename and enter its interface. 3. Click the "Operations" tab at the top. 4. Fill in the "Rename Table to:" input box. 5. Click the "Execute" button to complete the renaming. After renaming, all data and structures remain unchanged, but you need to ensure that the new table name is not occupied in the database and that the application, view, trigger or foreign key dependencies that reference the table need to be manually updated. Users must have ALTER and DROP permissions to perform this operation.

Sep 02, 2025 am 12:03 AM

重命名表

How to Use MongoDB with Python for Data Analysis

MongoDB and Python can efficiently analyze unstructured data, and PyMongo and pandas libraries need to be installed; 2. Connect the local or Atlas database through PyMongo to access the specified database and collection; 3. Use find() to query the data and convert it to pandasDataFrame to clean the inconsistent fields; 4. Use pandas for grouping, statistics and other analysis, and the results can be stored back to MongoDB or exported to CSV; 5. It is recommended to manage memory for large data sets and index them to improve query performance.

Sep 01, 2025 am 08:48 AM

How to get a random row from a MySQL table?

Forsmalltables,useORDERBYRAND()LIMIT1asitissimpleandeffective.2.Forlargetableswithfewgaps,usetherandomIDmethodbyselectingarandomIDbetweenMINandMAXandfetchingthefirstrowwithWHEREid>=random_valueORDERBYidLIMIT1,whichisfastandefficient.3.Forlargetabl

Sep 01, 2025 am 08:18 AM

mysql 隨機(jī)行

How to count the number of rows in a table in SQL?

To count the number of rows in the table, you should use the COUNT() function; 1. Use SELECTCOUNT()FROMtable_name to count all rows containing NULL values; 2. Use SELECTCOUNT(column_name) to count only rows whose columns are not NULL; 3. Use the WHERE clause to add conditional filter counts, so when you want to get the total number of rows, you should use SELECTCOUNT(*)FROMyour_table to end.

Sep 01, 2025 am 08:06 AM

What is the maximum number of columns in a MySQL table?

MySQL 8.0.19 and above support the InnoDB table up to 4,096 columns, but the actual number of available columns is limited by row size (about 8,000 bytes), and requires the use of Dynamic or Compressed row format; the upper limit of earlier versions was 1,017 columns; the MyISAM engine supports 4,096 columns but is limited by 65,534 byte row size; despite this, more than tens of columns should be avoided during design, and it is recommended to optimize the structure through normalization, association tables or JSON columns to ensure maintainability and performance.

Sep 01, 2025 am 08:00 AM