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Technical Articles

Database

How to connect to a MySQL server using Python

To connect to MySQL server using Python, you need to first install mysql-connector-python or PyMySQL library, and then use the correct credentials to establish the connection. 1. Install the library: Use pipinstallmysql-connector-python or pipinstallPyMySQL. 2. Use mysql-connector-python connection: pass in host, port, user, password and database parameters through mysql.connector.connect() method, and handle exceptions in the try-except block. Execute after the connection is successful.

Sep 07, 2025 am 01:09 AM

How to delete data from a table in MySQL

To delete data from MySQL tables, you must use DELETE statements and operate with caution. 1. The basic syntax is DELETEFROMtable_nameWHERE condition; it must include a WHERE clause to specify the deletion condition, otherwise all rows will be deleted, such as DELETEFROMusersWHEREid=5; records with id 5 will be deleted. 2. Multiple rows can be deleted through wider conditions, such as DELETEFROMusersWHEREage

Sep 07, 2025 am 01:00 AM

mysql delete data

What is the difference between Redis Sentinel and Redis Cluster?

RedisSentinelandRedisClusterdifferinarchitecture,failurehandling,scalability,andclientsupport.1.Sentinelusesanexternalprocessforfailoverinamaster-slavesetup,whileClusterusesadecentralized,shardedarchitecturewithnodesmanagingdataandfailures.2.Bothoffe

Sep 07, 2025 am 12:53 AM

How to perform conditional logic with IF-ELSE in SQL?

SQL uses CASE expression to implement conditional logic, and there is no direct IF-ELSE syntax in standard queries; 1. Use CASE to return different values ??according to conditions, such as grouping by age; 2. Use CASE to combine dynamic filtering in WHERE, but it is recommended to use Boolean logic to improve readability; 3. Use CASE to customize the sorting priority in ORDERBY, such as job sorting; 4. MySQL supports IF() function to simplify binary judgment, but is not standard SQL; 5. Stored procedures can use IF...ELSE to control the process, limited to process languages ??such as T-SQL; In short, conventional queries should use CASE to process conditional logic to ensure that conditions are mutually exclusive and overwrite boundary conditions such as NULL to enhance query dynamics

Sep 07, 2025 am 12:29 AM

sql if-else

How to format the output of the mysql command-line client

Use\Gtodisplayresultsverticallyforbetterreadabilityofwiderows,especiallywhenviewingsinglerecordswithmanycolumns;2.Use--tableor--verticalcommand-lineoptionstoforcedefaulttableorverticaloutputwhenstartingtheclient;3.Use--batch(-B)modetoproducetab-separ

Sep 06, 2025 am 07:24 AM

How to create a user in MySQL?

To create a MySQL user, use the CREATEUSER statement and grant permissions. 1. Create a user using CREATEUSER'username'@'host'IDENTIFIEDBY'password'; such as 'john'@'localhost' or 'anna'@'%'. 2. Grant necessary permissions through statements such as GRANTALLPRIVILEGESONdatabase_name.*TO'user'@'host'; or GRANTSELECT. 3. Execute FLUSHPRIVILEGES; make the permissions take effect. 4. It is recommended to use a strong password, follow the principle of minimum permissions, and refer to it if necessary

Sep 06, 2025 am 06:53 AM

mysql Create user

How to use variables in MySQL stored procedures

DeclarevariablesusingDECLAREatthestartofablockwithdatatypeslikeINT,VARCHAR,etc.,andoptionalDEFAULTvalues.2.AssignvaluesusingSETforexpressionsorSELECT...INTOforqueryresults,ensuringthequeryreturnsonerow.3.UsevariablesincontrolstructureslikeIF,CASE,orl

Sep 06, 2025 am 06:42 AM

mysql stored procedure

How to append a value to an existing string using APPEND?

The way to implement string appending in programming varies from language to system. There are several common methods: 1. Use the APPENDkeyvalue command in Redis to directly append content to the string key. If the key does not exist, create an empty string first and then append; 2. Use s ="value" in Python to implement string appending, or use io.StringIO to improve the performance of a large number of splicing operations; 3. Use str ="value" to append in Shell scripts, but be careful that variable assignments cannot have spaces. In addition, Redis's APPEND is atomic operation, suitable for concurrent environments; Python frequently splicing is recommended

Sep 06, 2025 am 06:40 AM

How to find the SID from a SPID in Oracle

TofindtheSIDfromagivenSPIDinOracle,usetheV$SESSIONandV$PROCESSviewswithajoinonpaddr=addr;1.RunSELECTs.sid,s.serial#,s.username,s.program,p.spidFROMv$sessionsJOINv$processpONs.paddr=p.addrWHEREp.spid='12345';replacing'12345'withtheactualSPIDtogettheco

Sep 06, 2025 am 05:58 AM

oracle SPID

What is the difference between LEFT JOIN and RIGHT JOIN in MySQL?

LEFTJOIN retains all rows on the left table, and RIGHTJOIN retains all rows on the right table. The two can be converted to each other by swapping the table order. For example, SELECTu.name, o.amountFROMuserssuRIGHTJOINordersoONu.id=o.user_id is equivalent to SELECTu.name, o.amountFROMordersoLEFTJOINuserssuONu.id=o.user_id. In actual use, LEFTJOIN is more common and easy to read, so RIGHTJOIN is less used, and the logic should be clear when selecting.

Sep 06, 2025 am 05:54 AM

mysql join

How to find constraints on a table in SQL?

To find the constraints of a table, different methods need to be used according to the database system: 1. Use INFORMATION_SCHEMA.TABLE_CONSTRAINTS to query the constraint type, which is suitable for MySQL, SQLServer and PostgreSQL; 2. Use SHOWCREATETABLE in MySQL to quickly view all constraints, or query INFORMATION_SCHEMA to obtain primary key, foreign key and other information; 3. It is recommended to use pg_constraint system table in PostgreSQL, and query constraint details through conrelid='table name'::regclass; 4. You can use it in SQLServer to query the constraint details through conrelid='table name'::regclass; 4.

Sep 06, 2025 am 05:48 AM