
SQL?? ??? ???? ???? ??? ??????
useinsert ... selectwherenotexiststoinsertonlyifnoduplication -posplice -posplice -posplice -insucportexists;
Aug 07, 2025 pm 09:34 PM
SQL?? ? ??? ?? (IQR)? ???? ??? ??????
TOCALCULATEIQRINSQL, usePercentile_cont (0.25) ? Percentile_Cont (0.75) Inpostgresql, SqlServer, Ororacletogetq1andq3, Thensubtractq 1fromq3toobtaintheiqr; 2.inmysql, wastPercentile_contisnotavailable, ???? q1andq3usingrow_number () Withpercentile ?? Row
Aug 07, 2025 pm 09:32 PM
SQL?? ?? ? ????? ??? ??? ???? ??? ??????
usegeographyforglobal, ?? ?? ??, GGEOMETORCOLOCAL, ???, ???;
Aug 07, 2025 pm 09:28 PM
SQL ???????? ??? ?? ?? ? ??
?? ??? ??, ?? ??? ???, ?? ?? ? ?? ?? ????? ????? ?????. ?? ?? : 1. ??? ?? ?? ???? ?? ?? ??? ?? ???? ??; 2. ?? ??? ?? ?? ? ??? ??; 3. ?? ?? ??? ?? ? ??? ??? ?? ???? ?????. 4. ?? ??? ?? ??. MySQL? ??? ??? ?? ?? ?? ??? ??? ?? Delimiter? ???? ?? ??? ???? ???? ??? ?? ??? ???? ???? ?? ??? ?????. ?? ? ? ?? ? ? ?? ?? ??? ???? ?? ?????? ??? ?? ???? ?????. ?? ?? ?? : ?? ??? ?? ?? ?? ?? ??, ??? ????? ????, ?? ??? ????, ?? ???? ???? ??? ???
Aug 07, 2025 pm 08:49 PM
SQL?? ???? ???? ??? ??? ??? ??????
?, ???? ???? ??? SQLServer ? PostgreSQL?? ?? ? ????. 1. SqlServer?? ReturnStable? ???? CreateFunctionDbo.getemployeesByDepartment (@DepTidint) ReturnStableReturn (SelectemployeeId, ??, ??, DepartmentIdfromeDepartmentID =@deptid)? ?? ??? ??? ? ??? ????. 2. ?? ?? ??? ?? returns@ta? ??????
Aug 07, 2025 pm 08:47 PM
MySQL?? ?? ???? ???? ??
TOSETADEFAULTVALUEWHENCREATINGATABLE, USETHEDEFAINGKEYWORDINTHECOLUMNDEFINITION, SALSDEFAULTCURNTIVERENT_TIMESTAMP.2.TOADDORCHANGEADEFAULTONECOLUMN, USEALSTABLESARESALCOLSTATUSTDEFAULT'INCATIVE'INMYSQL8.0.0.0
Aug 07, 2025 pm 08:44 PM
??? MySQL ???? ???? ???
?? CheckTable ?? ?? MyIsamchk ??? ???? ???? ?????? ??? ?? ?? ? ?? ??? ?? ?? ??? ??????. 2. MyISAM ???? ?? RepairTable ??? ????? MyISAMCHK-R-F ????? ???? ?? ? ? ????. 3. InnoDB ???? ?? MySQL? ?? ???? ???? ???? ???? ????? InnoDB_Force_Recovery? ???????. 4. ??? ???? ???? ??????? ???? ???????. 5. ?? ??? ????? InnoDB ?? ??? ?? ??? ???? ???? ??, ??? ???, ????? ?? ? ??? ??? ?????????. ?? ?? ??? ?? ???????
Aug 07, 2025 pm 08:24 PM
SQL? ????? ?? ???? ?????? ??? ??????
SQL ????? ?? ???? ??????? ???? ?? ???????. 1. ?? ???? ????? updatetable_name? ??????. 2. SetColumn1 = value1, column2 = value2? ???? ? ?? ?????. 3. ???? ? ?? WHER ???? ???????, ??? ??? ?? ???? ???????. 4. ???? ???? ?? ??? ?? ??? ? ??? ?; 5. ??? ?? ? ? ??? ?????? ??? ????? ???? ?? ????. 6. ?? ? ?? ?? ??? ???? ? ? ??? ?? ?? ?? ??? ?????. ?? ????? ??? ?? ?? ?? ????? ??????.
Aug 07, 2025 pm 08:13 PM
Show ProcessList? ???? MySQL?? ???? ??? ?? ??
ToseecurrentlyrunningqueriesinMySQL,usetheSHOWPROCESSLISTcommand;thisdisplaysactivethreadswithdetailslikeuser,host,querystate,andexecutiontime,whereIdisthethreadID,Usertheaccountrunningthequery,Hosttheclientaddress,dbtheselecteddatabase,Commandtheope
Aug 07, 2025 pm 07:48 PM
MySQL? ?? ?? ?? ???? ?? ??? ?????
AcingAnconnectionPoolwithMySqlimProvesperformanceByingExistingConnections, OverHeadoFeateDConnectionStablishing ? LowinglowingLatency.2.ItenablesBetterResourCemanagementConCurrentConnection, TheDatabaseFromHittingMax? ?????
Aug 07, 2025 pm 07:42 PM
MySQL?? IN ???? ???? ??
IN ???? ???? ?? ? ?? ??? ????? ???? ??????. 1. ??? ??? ?? ??? ??? ???? ????? ? ??????. 2. ?? ?? ???? ?? ???? ??? NULL? ????? ??? ??? ? ?????????. 3. ?? ???? ?? ??? ?? ??? ???? ID ??? ?? ?? ?? ?? ??? ?? ???? ??? ? ????. 4. ?? ???? ?? ?? ??? IN? ???? ?? ????? ???? ??? ?? ????. ?? ?? ?? NOTIN ? NULL? ?? ? ??? ?? ??? ??? ?? ???? ???????. ? ????? ??? ?? ?? ???????. ???, ?? ? ????? ???? ??? ? ? ? ?? ??????? ???????.
Aug 07, 2025 pm 07:21 PM
SQL?? ?? ???? ???? ??? ??????
Altertable ?? ???? ??? ??? ??????. 1. ? ?? : altertabletable_nameaddcolumn_namedata_type [?? ??]; 2. ? ?? : AltertableTable_namedRopcolumncolumn_name (???? ????? ?????). 3. ? ??? ?? ?? : mySQL? ?? ??, postgresql/sqlserver/oracle? ?? altercolumntype; 4. ? ??? ? : MySQL ? Postgresql, SQLSE ? Renamecolumn
Aug 07, 2025 pm 07:16 PM
SQL?? ?? ? ???? ??? ??????
thepurposeofthedistinctkeywordinsqlistoremovedUplicaterOwsfromtheresultset, returningOnlyUniqueValues.1.distinctFiltersOutRepeatedCombinationSofValuesInthectectionColumns
Aug 07, 2025 pm 07:09 PM
SQL? ???? ??? ??? (CTE)? ???? ??? ??????
ctesimprovesqlreadabilityandsimplifycomplexqueriesbreakingthemintologicalSteps.1
Aug 07, 2025 pm 07:07 PM
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