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Technical Articles

Database

What is the difference between ZREM and ZREMRANGEBYSCORE?

The difference between ZREM and ZREMRANGEBYSCORE is that the deletion method is different. 1. ZREM is deleted by member, used to remove one or more designated members, and does not care about their scores, and is suitable for deleting specific users or cheating entries; 2. ZREMRANGEBYSCORE is deleted by fraction range, suitable for batch cleaning of low-score or expired data, and supports open and closed intervals; both support multiple deletion and no errors are reported, but it is recommended to execute during low peak periods when deleting a large amount of data in performance.

Sep 09, 2025 am 04:10 AM

redis

How to handle character encoding issues like UTF8 in MySQL?

The utf8mb4 character set must be used to ensure that MySQL correctly handles UTF-8 encoding, including emoji and multilingual characters, because MySQL's utf8 is a pseudo-UTF-8, which only supports up to 3 byte characters and cannot store 4 byte characters; while utf8mb4 supports complete UTF-8 encoding, so CHARACTERSETutf8mb4COLLATEutf8mb4_unicode_ci should be explicitly set at the database, table, and column levels to obtain accurate sorting and comparison capabilities; at the same time, the default character set of client, mysql and mysqld parts must be set to utf8mb4 in the MySQL configuration file, and the client character set handshake should be skipped to strengthen the

Sep 09, 2025 am 04:04 AM

mysql utf8

How to perform union and intersection on Sorted Sets? (ZUNIONSTORE, ZINTERSTORE)

How to handle union and intersection of SortedSet in Redis? Use the ZUNIONSTORE and ZINTERSTORE commands to calculate the union and intersection of multiple ordered sets, and store the results in a new key; 1. ZUNIONSTORE is used for union, and the score of each member is the sum of its scores in each set by default. Weights can be set through WEIGHTS, and AGGREGATE specifies the aggregation method (SUM, MIN, MAX); 2. ZINTERSTORE is used for intersection, and only all members that exist in the specified set are retained, and the scores are aggregated according to the configuration; 3. Both commands can set weights and aggregation methods, which are suitable for ranking mergers, multi-dimensional data filtering and other scenarios.

Sep 09, 2025 am 03:37 AM

How to set up replication in MySQL

Configure the server-id of the master server, enable binary logs and set log format; 2. Create a dedicated user for replication and grant permissions; 3. Configure the unique server-id of the slave server; 4. Get the binary log file name and location on the master server; 5. Execute the CHANGEREPLICATIONSOURCETO command on the slave server and start replication; 6. Verify the replication status through SHOWREPLICASTATUS to ensure that the IO and SQL threads run normally and have no errors; 7. If the master library already has data, it needs to be exported using mysqldump and imported into the slave library to ensure data consistency, and finally realize master-slave data synchronization.

Sep 09, 2025 am 03:34 AM

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