SQL? ?? ???? ???? ??
usereplace (???, substring_to_replace, replacement_string) toreplacealloccurnsofasubstringinsql.2.forpermanentupdates, applyReplace () inanupdatestatement.3.bemindfulofcasesensitivity : mysqliscase-sensive, sqlserverdeperdoncollation, andpostgresqlreq
Aug 11, 2025 pm 11:10 PM
Oracle? Varchar2? Char? ???? ??????
SpacestOfillTheDefinedLength? whiled-lengthandpadswithpacestofillTheDefinedLength, whilevarchar2isvariable-lengthernyusesspaceneed.2.varchar2ismorestorage-efficientforvarying-lengthdata, asitdoesnotpad.3
Aug 11, 2025 pm 11:00 PM
SQL ???? ???? ??? ??????
SQL? ???? ???? ???? ??? ?????? ????? ????. ?? ????? ???? ?? CONCAT ??, ?? ??? ??? (||) ? Plus Operator (); 1. concat () ?? ?? : MySQL, postgresql9.1, sqlserver2012, sqlite ? oracle12c? ??? ??? selectConcat (FirstConcat (first_name, ', last_name) asfull_namefromusers?? ???? ?? null ?? ? ????? ?????. 2. ||? ?????? ??? : PostgreSQL, Oracle ? SQLITE ??, ??? SE???.
Aug 11, 2025 pm 10:56 PM
SQL? ???? ?? ??? ?????? ??? ??????
insqlserver, useupdatestatisticstable_nameorexecsp_updatestatsforalltables; 2.inpostgresql, useanalyzetable_nametoupdatestatisticsmentally;
Aug 11, 2025 pm 10:48 PM
MySQL?? ??? ??? ??? ???? ??
????? MySQL? Select Query? Case Insensivity ?? ?? (? : UTF8MB4_General_CI)? ??? ?? ?? ??? ???? ????. ??? ??? ??? ????? ?? ??? ??? ? ????. 1. Select*ourShowsHowsHowshowsBinaryUserName = 'Johndoe'? ?? ?? ??? ?? ?? ???? ??????. 2. Collate ?? ???? WhereSernameCollateUtf8mb4_bin = 'Johndoe'? ?? ??? ??? ?? ??? ??????. 3. ?? ???? ????? ??? ? ?? ???? ??? ?? ???? ?????.
Aug 11, 2025 pm 10:39 PM
Linux ???? Redis? ??? ? ?? ?? ??? ??????
Linux ???? Redis? ???? ????? ?? ??? ??????. 1) Redis? ?? ??? (127.0.0.1)? ??????. 2) ??? ????? ??????. 3) Redis? ??? ?? ???? ??????. 4) VPN ?? SSH ??? ???? ???? ??? ?????. 5) ??? ??? ?? ?? ? ????? ???? ?????. 6) SSL/TLS? ???? ??? ??? ??????. 7) ?? ??? ?????? Redis? ????? ????????. 8) Redis ??? ?????? ??? ?????. ? ??? Linux? ?? Redis? ?? ? ???? ???? ??? ? ??? ???? ???? ? ??????.
Aug 11, 2025 pm 10:37 PM
MySQL?? ???? ??? ?? ??
tofindthesizeofescifictibleInmysql, querytheInformation_schema.tablessByPlacing'Your_database_name'and'your_table_name'intheprovidedSqlstatementTogetTHETOTALSIZEINMB.2.TOLISTALLSTALLISTABASERDBYSIZE, USETHEMATION_SCHATERMEMA.TCHEATHETHEN, USETHEMATION_SCHATERMEA
Aug 11, 2025 pm 10:24 PM
MySQL? ???? ???? ???? ??
InsertInto ?? ???? MySQL ???? ???? ??????. 1. ?? ??? ??? ????. insertinto ??? ?? (? 1, ? 2, ...) ? (? 1, ? 2, ...); 2. ?? ?? ?? ? ? ?? ?? ?? ???? ?? ?? ?? ?? ?? ? ? ????. 3. ?? ?? ???? ???? ????? ?? ? ? ?? ? ??? ?? ? ? ????. 4. ? ??? ?? ?? ???? ?? ?? ? ? ???, ??? ?? ???? ???????, ?? ?? ?? ???? ?? NULL? ???? ??? ??? ??? ????. 5. insertignore? ???? ?? ??? ???? ???? ??? ????? onduplicatekeyUpdate? ?????. 6. ?? ???? ?? ? ?? ??, ??? ?? ?? ?? ? ??? ??? ??? ?????.
Aug 11, 2025 pm 10:15 PM
'MySQL Server? ??????'??? ???? ??
??, ??? ?? ??? ?? ???? ???? ?? Wait_Timeout ? Interactive_timeout? ?? ???? ?????. 2. ??? ??? ??? ???? ?? Max_allowed_packet ?? ??? ?????. 3. ?? ?? ???? ???? ?? ??? ??? ??? ?? MySQL ?? ?? ? ??? ???? ??????. 4. ?? ???? ???? ?? ?? ?? ? ?? ? ?? ????? ?????. 5. ???, ??? ?? ?? ??? ?? ?? ??? ???? ?? ? ??? ????? ???? ??? ?????.
Aug 11, 2025 pm 09:57 PM
MySQL ?????? ? ???? ??? ?? ??? ??????
Tocheckthesizeofescificdatabase, useAselectQuerywithwheretable_schema = 'your_database_name'meTofilterByDatabasEname.2.TolistAllDatabases? ?? withtheirsized, runAgroupByQueryOntable_scheMawithoutaWhereClaUseanUseanBysizeScending.3
Aug 11, 2025 pm 09:51 PM
MySQL?? ?? ?? ???? ??? ??????
themoscommonlyousedjointypesinmysqlareinnerjoin, ?? ??, ??? ?? ? ????? ? ?? ??, extermininghowsfromtwoormoretablesarecombinedbasedonmatchingcolumnvalues; innerJoineTurnSonlymatchingrows, leftjoinincludesllowsfromthefthithtn
Aug 11, 2025 pm 09:45 PM
mysqldump? ???? ??????? ???? ??
MySqlDump? ???? ???? ??????? ????? ?? ?? ?? ? ?? ??? ????????. 1. ??? ???? ?? ??????? ???? MySqlDump-uusername-pdatabase_name> backup.sql, ???? ??? ????? ???? ?????. ?? ? SQL ???? ??????? ???? ? ??? ?? ??? ?? ? ???? ???? ????. 2. ?? ??????? ??? ? mysqldump-uusername-p-databasesdb1db2> multip_dbs_backup.sql? ??-databases ??? ???? ?? ???? ??????? ???? ?? ?????. 3. ?? -
Aug 11, 2025 pm 09:44 PM
SQL?? ???? ????? ????? ??? ??????
???? ??? ?? ??? ????? ?? SQLServer ??? ?????? ?????? ??? ??? ?? ??? ???????. 1. ???? 10%??? ?? ??? ???? ????. 2. ???? 10%?? 30% ?? ? ?, ??? ?? alterindexindex_nameontable_namereorganize? ??????. 3. ???? 30%??? ?? AlterIndexIndex_nameontable_namerebuild? ???? ???? ?? FillFactor, Sort_in_TempDB ? ???? ?? ??? ???? ????? ??? ? ? ????. 4. sys.dm_db_inde? ?? ? ? ????
Aug 11, 2025 pm 09:23 PM
LAG () ? lead () ??? ???? ??? ??????
lag () ? lead ()? ?? ?? ?? ? ?? ?? ? ??? ?? ???? SQL? ? ?????. 1. LAG (?, ???, ???)? ?? ?? ???? ?? ? ?????. ???? ???? ? ?? ?, ?? 1 ?, ???? ?????. ?? ???? ?? ?? ?? ?????. 2. ?? (?, ???, ???)? ?? ?? ???? ?? ? ???? ?? ?? ??? LAG ()? ?????. 3. Orderby? ???? ??? ???? ??? ?? ? ?? ?? ???? ?? ? ? ??? ??????. 4. PartitionBy? ???? ??? ???? ???? ?? ??? ???? ???? ???????. 5. ? ?? ??? ??? ?? ???? ?????.
Aug 11, 2025 pm 08:14 PM
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