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Home

Technical Articles

Database

How to truncate a table in MySQL

TotruncateatableinMySQL,usetheTRUNCATETABLEstatement;thisremovesallrowsquickly,resetsauto-incrementcounters,andkeepsthetablestructureintact.1.ExecuteTRUNCATETABLEtable_name;forexample,TRUNCATETABLEusers;2.NotethatitisfasterthanDELETEasitisaDDLoperati

Aug 08, 2025 pm 05:27 PM

How to lock a table in SQL?

InMySQL,useLOCKTABLEStable_nameREAD/WRITEandUNLOCKTABLEStorelease;2.InPostgreSQL,useBEGIN;LOCKTABLEtable_nameINACCESSEXCLUSIVEMODE;thenCOMMIT;3.InSQLServer,useBEGINTRANSACTION;SELECT*FROMtable_nameWITH(TABLOCKX);thenCOMMIT;4.InOracle,useLOCKTABLEtabl

Aug 08, 2025 pm 05:25 PM

How to create a database link in SQL?

The steps to create a database link in Oracle are as follows: 1. Use the CREATEDATABASELINK statement to define the link name, remote user name password and connection string; 2. Ensure that the network is accessible and configured TNS or use a complete connection descriptor; 3. Have CREATEDATABASELINK permission; 4. You can test the connection through SELECT*FROMdual@link_name; 5. Use DROPDATABASELINK to delete the link. This operation supports cross-database access to objects and must comply with security specifications.

Aug 08, 2025 pm 05:13 PM

How to calculate a running total in SQL?

Using the SUM() window function and working with ORDERBY is the best way to calculate the total of SQL runs. The specific steps are: 1. Use SUM(column_name)OVER(ORDERBYsort_column) syntax to implement cumulative summing; 2. If you need to calculate separately by group (such as category or month), add the PARTITIONBY clause; 3. Make sure that ORDERBY exists in OVER() to ensure row-by-line accumulation; 4. The default window range is from the first line to the current line, and there is no need to explicitly specify ROWSUNBOUNDEDPRECEDING; 5. This method is suitable for PostgreSQL, SQLServer, Oracle, MySQL8.

Aug 08, 2025 pm 05:09 PM

How to perform a point-in-time recovery in MySQL

Enablebinaryloggingbyconfiguringlog-binandserver-idinmy.cnf/my.iniandrestartMySQL,confirmingwithSHOWVARIABLESLIKE'log_bin';2.Takeafullbackupusingmysqldumpwith--single-transaction,--flush-logs,and--master-data=2toensureconsistencyandrecordbinlogpositi

Aug 08, 2025 pm 05:05 PM

mysql 時間點恢復

What is Galera Cluster for MySQL and how does it provide high availability?

GaleraClusterforMySQLprovideshigh-availabilitythroughsynchronousmulti-masterreplication,ensuringdataconsistencyandminimaldowntime.1)Itworksbyexecutingtransactionslocally,broadcastingthemcluster-wide,certifyingforconflicts,andapplyingtheminthesameorde

Aug 08, 2025 pm 04:58 PM

High availability

How to create a new user and assign roles in SQL?

The method of creating and assigning roles varies from database management system; 2. In MySQL, use CREATEUSER to create users, and use GRANT to assign permissions or roles. MySQL8.0 supports role functions; 3. In PostgreSQL, CREATEUSER or CREATEROLE can create logged-in users, and grant permissions or roles through GRANT; 4. In SQLServer, first use CREATELOGIN to create server-level login, then use CREATEUSER to create database-level users, and finally assign roles through sp_addrolemember; 5. Different systems need to pay attention to host restrictions, differences between roles and permissions, and password security

Aug 08, 2025 pm 04:48 PM

How to find the size of a database in MySQL

To view the size of the MySQL database, 1. You can obtain the total size of the specified database (including data and index) by querying the information_schema database, use SUM (DATA_LENGTH INDEX_LENGTH) and convert it to MB; 2. When querying all databases, arrange it in descending order of total size to identify the database that consumes the most space; 3. View the size distribution of each table in a single database, which can help discover large tables that need to be optimized. All queries are safe and fast, because information_schema only stores metadata.

Aug 08, 2025 pm 04:01 PM

How to migrate from Oracle to MySQL

AssesscompatibilitybyevaluatingdifferencesinSQLdialects,datatypes,andarchitecture,inventoryingdatabaseobjects,andusingtoolslikeMySQLMigrationToolkitorAWSDMS.2.ConvertschemabytransformingDDLstatements—replaceOraclesequenceswithAUTO_INCREMENTorMySQL8.0

Aug 08, 2025 pm 03:49 PM

How to get the schema of a table in SQL?

UseDESCRIBEtable_nameinMySQLorSQLiteforaquickoverviewofcolumndetails;2.QueryINFORMATION_SCHEMA.COLUMNSwithappropriatefiltersforTABLE_NAMEandTABLE_SCHEMA/TABLE_CATALOGtogetportable,standardSQLschemainformationacrossMySQL,PostgreSQL,SQLServer,Oracle,an

Aug 08, 2025 pm 03:37 PM

How to implement a search functionality with LIKE operator wildcards in MySQL?

To implement the search function of using LIKE operators in MySQL, you need to master the usage of wildcard % and \_, and combine preprocessing statements to ensure security and performance. The specific steps are as follows: 1. Use % to match zero or more characters, such as '%keyword%' to find any text containing keywords; 2. Use \_ to match a single character, such as '\_ohn' to match a four-letter name ending with "ohn"; 3. Use preprocessing statements to bind parameters in back-end languages such as PHP to prevent SQL injection, such as using PDO's prepare and execute methods; 4. In order to implement case-insensitive search, you can use the LOWER() function to convert case uniformly or set appropriate words

Aug 08, 2025 pm 03:32 PM

mysql Search function

How to add a partition to an existing table in MySQL

For non-partitioned tables, the entire partition structure must be redefined using ALTERTABLE...PARTITIONBY. This operation will rebuild the table and may cause locking tables; 2. For partitioned tables, if they are of RANGE or LIST type, you can directly use ALTERTABLE...ADDPARTITION to add new partitions; 3. For HASH or KEY partitions, ADDPARTITION is used to increase the number of partitions and redistribute data; 4. When adding partitions, you must avoid definition conflicts, and operate during low peak periods and backup in advance to ensure data security and system stability.

Aug 08, 2025 pm 03:08 PM

mysql Partition Table

How to use the MIN function in MySQL

TheMIN()functioninMySQLreturnsthesmallestvalueinaset.1.Tofindtheminimumvalueinacolumn,useSELECTMIN(column_name)FROMtable_name;2.WithGROUPBY,itreturnstheminimumpergroup,suchasthelowestsalarybydepartment;3.Itworkswithdatestofindtheearliestdate;4.Combin

Aug 08, 2025 pm 03:05 PM

mysql min function

How to drop a table in SQL?

To delete tables in SQL, you need to use the DROPTABLE statement; 1. The basic syntax is DROPTABLEtable_name, which can permanently delete the table structure and data; 2. You can use DROPTABLEIFEXISTS to prevent errors when the table does not exist; 3. The deletion operation is irreversible, and you must ensure that the data has been backed up; 4. You need to check the dependent object to avoid destroying other database objects; 5. Some databases support CASCADE to delete dependent objects or RESTRICT to prevent deletion when there is a dependency, and you should be cautious about it before the operation.

Aug 08, 2025 pm 02:46 PM