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Technical Articles

Database

SQL

How to implement error handling with TRY...CATCH in SQL

Yes,TRY...CATCHinSQLServerallowsgracefulerrorhandlingbycapturingruntimeerrorsintheTRYblockandtransferringcontroltotheCATCHblock,wherebuilt-infunctionslikeERROR_MESSAGE(),ERROR_NUMBER(),andothersprovidedetailederrorinformation,enablingtransactionrollb

Aug 26, 2025 am 12:50 AM

How to select random rows from a table in SQL

To select random rows from SQL tables, you need to select methods according to the database system: MySQL uses ORDERBYRAND(), PostgreSQL and SQLite uses ORDERBYRANDOM(), SQLServer uses ORDERBYNEWID() or TABLESAMPLE, Oracle uses DBMS_RANDOM.VALUE or SAMPLE clause; for large tables, in order to improve performance, TABLESAMPLE or subquery-based offset technology should be used first to avoid full table sorting, but it should be noted that SAMPLE and TABLESAMPLE do not guarantee the exact number of rows, and the simple offset method may be inaccurate when there is a gap in the ID.

Aug 25, 2025 am 11:29 AM

sql 隨機(jī)行

How to use self join in SQL?

Aselfjoinisusedtojoinatablewithitself,typicallyforhierarchical,sequential,orcomparativeanalysiswithinthesametable.1.Useaselfjoinwhendealingwithhierarchicaldatalikeemployeesandmanagers.2.Applyittocomparerowsinthesametable,suchasfindingemployeesinthesa

Aug 25, 2025 am 10:45 AM

sql

How to clone a database in SQL?

ForMySQL,usemysqldumptoexportthedatabaseandimportitintoanewdatabasecreatedwithCREATEDATABASE;2.ForPostgreSQL,useCREATEDATABASEwiththeTEMPLATEoptionafterensuringnoactiveconnectionsexist;3.ForSQLServer,backuptheoriginaldatabaseandrestoreitunderanewname

Aug 25, 2025 am 10:04 AM

sql 數(shù)據(jù)庫(kù)克隆

How to find tables containing a specific column name in SQL?

To find a table containing a specific column name, you should query the information_schema.columns view; 1. Use standard SQL in MySQL, PostgreSQL and SQLServer: SELECTtable_name, table_schemaFROMinformation_schema.columnsWHEREcolumn_name='your_column_name'; 2. Pay attention to case sensitivity. PostgreSQL needs to match the case names with quotes. You can use LOWER() to implement case-insensitive search; 3. To cross databases in MySQL

Aug 25, 2025 am 09:58 AM

How to backup and restore a database using SQL commands?

MySQL backup uses the mysqldump command to export SQL files, and imports them through the SOURCE command or mysql command during recovery; 2. PostgreSQL uses pg_dump to export backup files and restore them through the psql command; 3. SQLServer uses the BACKUP and RESTORE commands of T-SQL to directly perform backup and restore operations; all methods need to ensure the consistent state of the database. It is recommended to regularly test the backup integrity and automate it with system tools to end with a complete sentence.

Aug 25, 2025 am 09:43 AM

SQL Static Code Analysis for Performance and Security

SQL static analysis can detect performance and safety hazards in advance. Its core role is to check statement structure, syntax specifications and potential risks through tools or manual inspection, so as to find performance problems such as unused indexes, full table scanning, and subqueries that are too deeply nested; security problems such as string splicing leading to SQL injection; and poor maintainability such as irregular naming and excessive complexity. Common performance problems include using SELECT*, performing function operations on fields in WHERE conditions, excessive or unoptimized JOINs, improper index use, etc. In terms of security, you need to pay attention to parameterizing all inputs, whitelist verification dynamic fields, avoid splicing keywords, and use minimal permission accounts. Recommended tools include SonarQube plugin, SQLint, RedgateSQ

Aug 25, 2025 am 09:27 AM

How to parse XML data in SQL?

Use the .nodes() method to split XML into rows by path; 2. Use the .value() method to extract node values ??and attributes, and you need to specify the data type and [1] to obtain scalar values; 3. When a namespace exists, you need to declare and use prefixes through WITHXMLNAMESPACES; 4. For optional or missing elements, .value() will safely return NULL; 5. OPENXML is an old method and is not recommended for new development. The parsing of XML data in SQLServer mainly relies on the .nodes() and .value() methods combined with XQuery expression to efficiently extract structured data, and the data type and namespace need to be correctly processed.

Aug 25, 2025 am 08:52 AM

How to implement a search for multiple keywords in SQL?

Multi-keyword search can be achieved using LIKE with AND or OR. OR means any keyword matching, and AND means all keyword matching, but the index cannot be used when wildcards are prefixed, and the performance is poor. 2. It is recommended to use full-text search to improve performance. In MySQL, MATCH(), AGAINST(), and other operators are used to accurately control the inclusion or exclusion of keywords under BOOLEANMODE. PostgreSQL uses to_tsvector and tsquery to support & (and), | (or) logic, and SQLServer uses CONTAINS or FREETEXT functions; 3. If you need to search across multiple columns, you can establish a joint FULLTEXT search for multiple columns.

Aug 25, 2025 am 08:01 AM

How to compare two tables to find differences in SQL?

UseFULLOUTERJOINtoidentifyunmatchedrowsbyjoiningonallrelevantcolumnsandfilteringwhereonesideisNULL,whichrevealsrowsmissingineithertableordifferingdata;2.UseEXCEPT(orMINUSinOracle)tocompareentirerowsetswhensupported,combiningwithUNIONALLtogetdifferenc

Aug 25, 2025 am 06:26 AM

How to rename a column in SQL

RenamingacolumninSQLrequiresusingdatabase-specificsyntax.InPostgreSQL,SQLServer2016 ,SQLite,andOracle9i ,useALTERTABLEtable_nameRENAMECOLUMNold_nameTOnew_name;inMySQL,useALTERTABLEtable_nameCHANGEold_namenew_namedata_type,specifyingtheexistingdatatyp

Aug 25, 2025 am 06:23 AM

sql 重命名列

How to generate a sequence of numbers in SQL?

Generating a sequence of numbers in SQL depends on the database system. The preferred method is to use built-in functions, and if not available, recursive CTE or cross-connect simulation. 1.PostgreSQL and ClickHouse support GENERATE_SERIES() or numbers() to directly generate sequences; 2. For unsupported databases such as MySQL

Aug 25, 2025 am 05:37 AM

How to select the first row in each group in SQL

To select the first row in each group, the most reliable method is to use the ROW_NUMBER() window function; group by PARTITIONBY and define the order with ORDERBY, and then filter rn=1 in the outer layer to get the first row in each group in the specified order, for example, SELECTFROM(SELECT,ROW_NUMBER()OVER(PARTITIONBYcustomerORDERBYorder_date)ASrnFROMorders)rankedWHERErn=1. This method is suitable for most modern SQL databases and can ensure the determinism of the result by adding secondary sorting keys. In PostgreSQL

Aug 25, 2025 am 04:19 AM

How to handle transactions in SQL?

TohandletransactionsinSQL,useBEGINtostart,COMMITtosavechanges,andROLLBACKtoundothemiferrorsoccur;1.BeginatransactionwithBEGINTRANSACTIONorSTARTTRANSACTION;2.ExecuteSQLstatementslikeINSERT,UPDATE,orDELETE;3.UseCOMMITtopermanentlyapplychanges;4.UseROLL

Aug 25, 2025 am 04:11 AM

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