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Technical Articles

Database

Oracle

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

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 import a table into Oracle

UseSQLLoaderforimportingdatafromflatfileslikeCSVbycreatingatargettable,preparingacontrolfile,andrunningsqlldrfromthecommandline;2.UseOracleDataPump(IMPDP)for.DMPfilesbycreatingadirectoryobject,grantingpermissions,andexecutingimpdpwithappropriateparam

Sep 08, 2025 am 06:12 AM

How to check tablespace size in Oracle

To check the Oracle tablespace size, SQL query must be performed using the data dictionary view; 1. Pass SELECTdf.tablespace_name,ROUND(SUM(df.bytes)/1024/1024/1024,2)AStotal_size_gb,ROUND(SUM(NVL(fs.bytes,0))/1024/1024/1024,2)ASfree_space_gb,ROUND((SUM(df.bytes)-SUM(NVL(fs.bytes,0)))/1024/1024/1024,2)ASused_space_gb,

Sep 08, 2025 am 03:54 AM

Oracle LISTAGG function example

The LISTAGG function is used to concatenate multiple rows into a single string, usually grouped by category; 1. Use LISTAGG (column, delimiter) to specify the columns and delimiters to be connected; 2. You must use WITHINGROUP (ORDERBY...) to define the connection order; 3. When aggregating by category, you need to use GROUPBY; 4. The default maximum length of the result is 4000 characters, and it is necessary to use ONOVERFLOWTRUNCATE to process; 5. You can safely truncate the extra-long string through ONOVERFLOWTRUNCATE...'WITHCOUNT and display the omitted count; this function is equivalent to MySQL's GROUP_CONCAT or

Sep 07, 2025 am 07:20 AM

oracle LISTAGG

How to find duplicate records in a table in Oracle

The most effective way to find duplicate records in Oracle tables is to use the GROUPBY and HAVING clauses in conjunction with the ROW_NUMBER() window function. 1. Use GROUPBY and HAVING to identify duplicate values, such as SELECTemail, COUNT()FROMemployeesGROUPBYemailHAVINGCOUNT()>1 to return duplicate email and its occurrence number; 2. To view the complete duplicate row, use ROW_NUMBER()OVER(PARTITIONBYemailORDERBYemployee_id) to assign row numbers to each group, filter rn&gt

Sep 07, 2025 am 06:42 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 DELETE and TRUNCATE in Oracle?

DELETEisaDMLcommandthatremovesrowsoneatatimewithindividuallogging,whileTRUNCATEisaDDLcommandthatdeallocatesdatapagesforfasterexecution.2.DELETEcanberolledbackwithinatransactionusingundologs,whereasTRUNCATEisgenerallynon-transactionalandirreversiblewi

Sep 06, 2025 am 05:45 AM

What are the different types of joins in Oracle?

ThemaintypesofjoinsinOracleare:1.INNERJOINreturnsonlymatchingrowsfrombothtables;2.LEFTJOINreturnsallrowsfromthelefttableandmatchedrowsfromtheright,withNULLsforunmatchedright-sidecolumns;3.RIGHTJOINreturnsallrowsfromtherighttableandmatchedrowsfromthel

Sep 05, 2025 am 08:17 AM

How to rebuild an index in Oracle

UseALTERINDEXindex_nameREBUILDtorebuildanindex,whichcreatesanewcompactversionandreplacestheoldone;2.Optionallyspecifystorageparametersliketablespaceorblocksizeduringrebuild;3.UseALTERINDEXindex_nameREBUILDONLINEtoallowconcurrentDMLoperations,thoughit

Sep 05, 2025 am 05:41 AM

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