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Technical Articles

Database

How to optimize LIKE queries with a leading wildcard in MySQL

Use reverse index to convert suffix searches into prefix searches, thereby improving performance using indexes; 2. For word-based searches, use FULLTEXT index to achieve efficient full-text search; 3. Use generated columns to pre-calculate and index the query values ??of fixed patterns in MySQL5.7; 4. For complex partial matching or frequent search requirements, external search engines such as Elasticsearch are used; 5. Optimize queries by combining index conditions, limiting the return results, and using overlay indexes to reduce the impact of full table scanning.

Sep 09, 2025 am 03:22 AM

Performance Tuning for High Throughput Writes in MongoDB

Use unordered batch writes (bulkWritewithordered:false) to improve write efficiency; 2. If the risk of data loss is acceptable, disable logs (j:false or global shutdown journal) to reduce I/O overhead; 3. Tune the WiredTiger storage engine to increase cache, enable compression and pre-slice to avoid hotspots; 4. Simplify the indexing strategy, create only necessary indexes to avoid excessive indexes to slow down writes; 5. Realize horizontal scaling through hash sharding, and distribute the write load to support high throughput. The core of optimization lies in batch processing, reducing persistence requirements, rationally configuring storage, controlling the number of indexes and timely sharding, thereby maximizing MongoDB write performance and ultimately achieving stable and efficient write-intensive w

Sep 09, 2025 am 03:01 AM

mongodb Performance optimization

How to sort by a custom order in SQL

Use CASE expressions to implement custom sorting in SQL. 1. Use ORDERBY and CASE to assign sorting weights to each value, which is suitable for all mainstream databases; 2. Use FIELD() function to simplify the syntax in MySQL, but the values ??that are not in the list need to be processed; 3. It is recommended to use ARRAY_POSITION() instead of POSITION() in PostgreSQL to avoid matching errors; 4. For frequently used sorting logic, it is easier to maintain for creating mapping tables and associated queries. This method ensures that the custom order takes effect accurately and supports multi-column sorting and outlier processing, ultimately achieving flexible and reliable sorting results.

Sep 09, 2025 am 02:55 AM

How to connect to a MySQL database using Java (JDBC)?

Add MySQLJDBC driver, and introduce JAR packages through Maven dependencies or manually; 2. Modern JDBC versions do not need to explicitly load the driver; 3. Use DriverManager.getConnection() method to establish a connection with the correct URL, username and password; 4. Automatically close resources and handle SQLException through try-with-resources; 5. Simple query test connections can be executed, such as SELECTNOW(); Common problems include driver not found, access denied, connection denied and time zone errors. You need to ensure that the driver is in the classpath, credentials, MySQL service is running and configured with appropriate time zone parameters. After the connection is successful, you can enter normally.

Sep 09, 2025 am 02:50 AM

How to increase upload file size in phpMyAdmin

To solve the problem of restricted uploading large SQL files by phpMyAdmin, you need to adjust the PHP configuration: 1. Edit the php.ini file, set upload_max_filesize, post_max_size, memory_limit and max_execution_time to larger values, and restart the web server; 2. If php.ini cannot be modified, you can use the php_value command to adjust the corresponding parameters in the .htaccess file of the phpMyAdmin directory, provided that the host supports it; 3. If it is still not feasible, you can divide the SQL file and use BigDump and other tools to import it in batches, or directly execute mys through the command line

Sep 09, 2025 am 02:49 AM

上傳文件大小

What is an Oracle view and how to create it?

AviewinOracleisavirtualtablebasedonaSQLquery,usedtosimplifyqueries,enhancesecurity,andmaintainconsistency.Itdoesnotstoredataitself,exceptformaterializedviewswhichphysicallystoreresults.Tocreateaview,usetheCREATEVIEWstatementfollowedbyaSELECTquery.For

Sep 09, 2025 am 02:46 AM

Database view oracle view

How to disable a trigger in SQL?

InSQLServer,useDISABLETRIGGERtrigger_nameONtable_nametodisableatrigger;2.MySQLlacksdirectsupport,souseauser-definedvariableflaginthetriggerlogicordropandrecreatethetrigger;3.InPostgreSQL,useALTERTABLEtable_nameDISABLETRIGGERtrigger_name;4.InOracle,us

Sep 09, 2025 am 02:45 AM

SQL Server Change Data Capture (CDC) Implementation

To enable SQLServerCDC, follow the steps. First, confirm the version support, and then enable it for the database and table respectively. When querying change data, use built-in functions and LSN ranges. Cleaning up data can be done with default or custom policies. 1. Enable CDC: USEYourDatabaseName; EXECsys.sp_cdc_enable_db; and then enable: EXECsys.sp_cdc_enable_table@source_schema='dbo',@source_name='YourTableName'; 2. Query change: Use cdc.fn_cdc_get_all_chang

Sep 09, 2025 am 02:42 AM

How to concatenate strings in SQL

The use of the CONCAT function is the safest string splicing method across databases. It can automatically treat NULL values ??as empty string processing; this function is supported in MySQL, PostgreSQL, SQLServer, Oracle and SQLite; PostgreSQL, Oracle and SQLite also support splicing using the || operator, where the result of NULL and string splicing is the string itself; SQLServer uses operators, but it should be noted that if any operand is NULL, the result is NULL, so it needs to be used with ISNULL or COALESCE functions to ensure security; in summary, in order to ensure portability and reliability of NULL value processing,

Sep 09, 2025 am 02:22 AM

How to update a table from another table in SQL

ToupdateatableusingdatafromanothertableinSQL,useaJOIN-basedUPDATEsyntaxspecifictoyourdatabasesystem:inMySQL,useUPDATEwithJOIN;inSQLServer,includetheFROMclauseafterSET;inPostgreSQL,useFROMwithWHEREtojoin;alternatively,useasubquerywithWHEREEXISTSforbro

Sep 09, 2025 am 02:21 AM

sql 表更新

How to export a database from phpMyAdmin

LogintophpMyAdminandselectthetargetdatabase.2.Clickthe“Export”tabandchoose“Custom”methodforfullcontrol.3.SetformattoSQL,ensure“Dumptablestructure”and“Dumpdata”arechecked,andenable“Saveasfile”forlargedatabases.4.Optionallyselectspecifictables,setchara

Sep 09, 2025 am 02:04 AM

What is Oracle RMAN and how to use it for backup?

RMANisOracle’sbackupandrecoverytoolthatenablesefficient,block-levelbackupswithminimalperformanceimpact.Itsupportsincrementalbackups,automatedoperations,andbothonlineandofflinebackups,whileintegratingwithdiskandtapestorage.Keystepsincludeconnectingvia

Sep 09, 2025 am 01:56 AM

How to Perform CRUD Operations in MongoDB

MongoDBCRUDoperationsuseinsert,find,update,anddeletemethods.First,insertdocumentswithinsertOne()orinsertMany().Then,retrievedatausingfind()orfindOne(),withoptionalfiltersandfieldprojections.Next,modifydocumentsviaupdateOne(),updateMany(),orreplaceOne

Sep 09, 2025 am 01:39 AM

How to Troubleshoot MySQL Replication Lag?

First, confirm the replication status, 1. Run SHOWSLAVESTATUS\G to check whether Slave_IO_Running and Slave_SQL_Running are Yes, whether Seconds_Behind_Master values ??are too high, and whether there is Last_Error; 2. Determine the delay type, if the IO thread is normal but the delay increases, it may be a bottleneck of SQL threads. If the IO thread stops, it may be a network or authentication problem; 3. Troubleshoot common causes and fixes, including: optimizing connection or compression protocols during network delay, upgrading hardware or adjusting InnoDB parameters during resource bottlenecks, enabling parallel replication during single-thread playback (set slave_paralle

Sep 09, 2025 am 01:24 AM

mysql Replication delay