MySQL? ?? ??? ??? ??????
mysqlprovideInteger, ??? ? ?? ? ??? ??? umericdatatypes; usetinyintforsmallrangesandflags, intforgeneralwholenumbers, decimalforexactvalueslikemoney ? bigintforlargenumbers, renuringoptimalstorageandpercorction.
Aug 23, 2025 am 05:48 AM
MySQL?? Bigint? Int? ???? ??????
bigintuses8bytesandsupportsvalues-9,223,372,036,854,775,808to9,223,372,036,854,775,807, whideintuses4bytesandsupports-2,14 7,483,648to2,147,483,647, kingbigintsuilableforlargernumbersincaseslikedikededsystemidsorlargecounters, intistissuffi
Aug 23, 2025 am 03:35 AM
MySQL?? json_extract ??? ???? ??
JSON_Extract ??? JSON ???? ??? ??? ???? ???? ? ?????. ?? JSON Path Syntax? ???? ?? ??? ?? ????. 1. ??? $, $ .key? ??? ????, ?? ? ?? ?? $ [index]? ?? ??? ?? []? ?? ??? ??? ?? ?? ?????. 2. JSON ?? ?? ?? ? ? ?? ? JSON ??? ?????. 3. ??? ?? ? ?, ???? ?? ?? ??? ????? [*]? ???? ?? ??? ???? ? ? ????. 4. ?? ? ??? ??, ??? ? ???? ? ??? ????? ???? ?? ???? ?????. 5. WHERE ??? JSON_EXTRANT ?? ->, -& g
Aug 23, 2025 am 02:48 AM
MySQL? ????? ?? ?? ???? ??? ??????
TodeletEduplicaterowsinmysql, useatemporarytableforcompatibility, row_number () inmysql8.0 tokeepthesmallestid, oraself-joinonderversionstoremoveduplicates wholepressvingoneinstance, andaddauniqueconstattopreduredureptructates;
Aug 23, 2025 am 12:11 AM
MySQL?? ?? ??? ???? ??
REPLEC () ??? ???? ???? ?? ???? ??? ?? (?? ???, ?? ??? ?? ??? ? ?? ? ??? ?? ???)? ?????. 2. Selectreplace ( 'HelloWorld', 'World', 'MySQL')? ?? ?? ???? ?? ??? ?? ? ? ???? 'HellomySql'? ?? ? ? ????. 3. ??? ???? ???? ? ?? ?? ???? ?? ??? '??'? '??'?? ??? ?? ?? replace ()? ?? ? ???? ?? ??? ? ????. 4. REPLEC () ??? ??? ???? ??? ???? ?? ?? ? ???? ?? ?? ??? ???????.
Aug 22, 2025 pm 02:09 PM
MySQL?? ifnull ()? ???? ???
ifnull () inmysqlreturnsthefirstexpressionifitispitisnull, OtherwiserEturnsthesecondexpression, gomingIdealforPelacingNullValues; forexample, ifnull (middle_name, 'n/a') ?? '/a'whenmiddle_nameisnull, ifnull, 0)
Aug 22, 2025 pm 02:00 PM
MySQL?? ?? ??????? ??? ?? ??? ??????
MySQL?? ?? ??????? ??? ??? Information_schema.tables?? ???? ???? SQL ??? ???????. sum (data_length index_length)? ?? ??? ??????? ? ??? ?? ???? MB ??? ??????. ?? ??, Sales_DB ??????? ??? ???? 100.00MB? ??? ??? ????? ??????? 100MB ??? ??? ???? ??? ?????. ? ??? ???? ???? ??? ? ??? ? ??? ???? ????? ??? ???? ????.
Aug 22, 2025 pm 12:41 PM
MySQL?? ????? ??? ??? ???? ??
tocloneatableStructure? ???? copyinganydatainmysql, youcanusethecreatetable ... likestatement.thismethodissimple, ?????, ?????, ?? ??, ?? ?? ? columndefaults.usecreatetable ... likecreatet
Aug 22, 2025 am 11:25 AM
MySQL ????? N ??? ?? ?? ?? ??? ??????
MySQL ????? n ?? ?? ?? ???? MySQL8.0 ??? ???? ?? Dense_Rank () ??? ???? ?? ?? ???? ???? ?? ????. ??? ??? LimitOffset (?? ?? ??) ?? ?? ?? ?? (?? ??? ?? ? ??? ?? ? ? ????)? ??? ? ????. Dense_Rank () ???? ??? ??? ??? ??? ???? ?? ??? ?? ?? ????? N-th ?? ?? ???? ????????. ?? ??? MySQL ??? ?? ???? ?? ????? ??? ?????????. ?? ??? ????? ?? ????.
Aug 22, 2025 am 11:03 AM
MySQL?? Group_Concat ???? ???? ??
Group_Concat () ???? ??? ???? ???? ???? ??? ?? ? ? ????. 1. ???? ???? ?? ??? ?? ??? ?? ???? ??????. '???? ???? ? ??? ???? ??? ? ????. 2. ???? ???? ??? ?? '|', space '', ?? ???? ?? '\ n'?? ??? ?? ??? '->'? ?????. 3. ???? ??? ??? ?? ???????? ?? ??? Group_Concat_Max_Len ??? ?? ???? SetSessionGroup_CONCAT_MAX_LEN = 100000?? ??? ? ????. 4. ???? ?? ?????
Aug 22, 2025 am 10:58 AM
MySQL?? ??? ????? ??? ?? ?????? ??
Tochecktheeventschedulerstatus, useshowvaribles like'event_scheduler ';. 2.toenableordisabletemporally, audestglobalevent_scheduler = onoroff, whiteficeptiveTectiveTilThenexTrestArt.3.3.ToEnableDisablePermanely, addevent_scheduler [mysqld)
Aug 22, 2025 am 09:59 AM
MySQL?? ?? ???? ?? ??
MySQL?? ?? ???? ???? substring () ??? ???????. 1. ??? ???? ??? ?????? : SelectSubstring ( 'HelloWorld', 5) Returns 'Oworld'; 2. ??? ?? ?? : SelectSubstring ( 'HelloWorld', 7,5) Returns 'World'; 3. ??? ???? ????? ???? ???? ?? : ??? ??, ?? ??? (???, ?? ( '@'inemail)) 1) ASDomainFromusers? ??? ??? ??? ?? ? ? ????. 4. ?? ?? ?? ?? : ?? ?? : ?? ??
Aug 22, 2025 am 07:32 AM
?? ??? ???? MySQL?? ???? ??? ??????
??? ?? helpingperformanceIssues.1.useexplainbeforeaselect, ??, ????, ??, orreplacestatement, mostcommonlywithselect
Aug 22, 2025 am 07:27 AM
MySQL?? ?? ?? ??? ???? ??? ??????
MySQL? FullOuterJoin? ???? ??? LeftJoin? RightJoin? UnivenAl? ???? ????? ? ? ????. ?, ?? Left Join Left Table ???? ?? ?? ??? ??? ???? ??? ???? ???? ?? ???? ????? ? ???? ?? ???? ????? ?? ??? ??? ?????.
Aug 22, 2025 am 06:43 AM
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