34 Task 9 One Person Can Only Vote for Three Vehicles A DayPHP动态网站开发项目教程课件

Project2OnlineVotingSystemSchoolofSoftware,ChengduPolytechnicLecturer:MuQichunTask9OnePersonCanOnlyVoteforThreeVehiclesADayProgrammingIntask8,wehaveknownthenumberofvotesthecurrentusercastedforonevehicleonthatday.Whilethistaskistoknowthenumberof

vehiclesthecurrentuserhasvotedforonthatday.

The

ruleisasfollows:excludingthecurrentvehicle

first,andthencheckhowmanyvehicleshavebeenvotedfor.

Ifitisturnedoutthattherearestill3vehicles,withthecurrentvehicle,therearetotally4,whichexceedsthelimit.

Therewillbebugsifthecurrentvotedvehicleisnotexcluded.

Ifthecurrentvehicleisnotincludedinthevehiclesthathavealreadybeenvotedfor,nofurthervotescanbemade.If

thecurrentvehicleisamongthevehiclesthathavebeenvotedfor,othervotescanbemade.(Ofcourse,italsodependsonwhetherotherconditionsaremet).Here,anewkeywordisused:groupby,whichisthesubtotalinexcel.TheGROUPBYstatementgroupstheresultsetaccordingtooneormorecolumns.

FunctionssuchasCOUNT,SUMandAVG

areusedinthegroupingcolumns.

Themostcommonscenarioisthestudent'sgradesheet,inwhichtherearemanyrecordsofrows,andcolumnsincludingnames,subjects,andscores.

Ifwecountthetotalscoreofeachsubjectaccordingtoperson,groupbystatementwillbeused.

Putnamecolumnaftergroupby,whichmeanstosummarizeaccordingtonames,andthenobtainthetotalscoreofeachpersonbysumfunction.

Obviously,

theaveragescoreforeachpersonwillbeobtainedbyavg.ProgrammingNext,invote.php,the

secondvotingrestrictionisadded.Thecodeisasfollows:Inrow3,wehavegrouped

accordingtovehicleIDs.Thenumberofvehiclesthecurrentuserhasvotedforonthatdayhasbeenknown.A

filterconditionisaddedtothewhere

clause.ThevehicleIDisnottheIDofthecurrentlyvotedvehicle,whichmeansthatthecurrentvotedvehicleisexcluded.ByaddingthecarIDfieldaftergroupby,wecangroupaccordingtovehicleIDs.Bydoingthis,thenumberofrecordsisthenumberofvehiclesthathavebeenvotedforinadditiontothecurrentvehicle.Inrow6,checkthevalueof$num,ifitisgreaterthanorequalto3,it

meansthatinadditiontothecurrentvehicle,3vehicleshavealreadybeenvoted

for.So

thecurrentvehicleisthe4thone,whichcannotbevotedconsequently.Sofar,wehave

hadtworestrictions.Solet'sthinkaboutit,invote.php,isthereapriorityforthetworestrictions?SummaryInthiscourse,wehaveaddedalimittovoting,thatis,onepersoncanonlyvoteforamaximumofthreevehiclesaday.Thisisjudgedbytherecordsinthevotedetail

table.Specialattention,pleasecarefullyunderstandthejudgmentlogic.As

multiplerestrictions,amongwhichtherearerelationship