Sebenzisa i-SQL COUNT ukubuyisela uluhlu olubanzi lweedatha
Iimpawu zeembuzo yingxenye ebalulekileyo yoLwimi lweeNzululwazi oluCwangcisiweyo (SQL). Ifumana idatha ngokusekelwe kwiikhrayitheriya ezithile ukusuka kwisiseko sedatha. Ungasebenzisa imibuzo ye-SQL - kuquka umsebenzi we-COUNT () - ukufumana zonke iindidi zolwazi ezivela kwisiseko sedatha.
Umsebenzi we-SQL COUNT () uncedo ngokukhethekileyo kuba kukuvumela ukuba ubale iirekodi zeenkcukacha ngokusekelwe kwiinkqubo ezichazwe ngumsebenzisi. Ungayisebenzisa ukubala onke amarekhodi etafileni, ubale amanani ayingqayizivele kwikholam, okanye ubale inani lamaxesha eirekhodi ezenzekayo ezihlangabezana nemigangatho ethile.
Eli nqaku lijonga kancinci nganye kwezi ziganeko.
Imizekelo isekelwe kwisiseko seNorthwind esisetyenziswa ngokuqhelekileyo, esoloko sihamba kunye nemikhiqizo yedatha yokusetyenziswa njengetitshala.
Nantsi ingqungquthela evela kwitheyibhile yomkhiqizo wedatha:
| ProductID | Igama lemveliso | UmthengisiID | UbungakananiPerUnit | Ixabiso lento | UnitsIntock |
|---|---|---|---|---|---|
| 1 | Chai | 1 | Iibhokisi ezili-10 x 20 iibhegi | 18.00 | 39 |
| 2 | Tshintsha | 1 | Iibhola ze-oz 24-12 | 19.00 | 17 |
| 3 | Isiraphu esisikiweyo | 1 | 12 - 550 iibhotile | 10.00 | 13 |
| 4 | I-Chef Anton's Cajun Seasoning | 2 | 48 - 6 izitya ze-oz | 22.00 | 53 |
| 5 | I-Chef Anton's Gumbo Mix | 2 | 36 iibhokisi | 21.35 | 0 |
| 6 | U-Grandm's Boysenberry Usasazeka | 3 | 12 - 8 izitya | 25.00 | 120 |
| 7 | Amalume aseMal Bob's Organic Omebileyo | 3 | 12 - 1 lb pkgs. | 30.00 | 15 |
Iirekhodi zokubala kwiThebhile
Umbuzo osisiseko kunokubala inani leerekhodi etafileni. Ukuba ufuna ukwazi inani lezinto ezikhoyo kwitheyibhile yomveliso, sebenzisa le mibuzo elandelayo:
HLOLA COUNT (*)
UMTHETHO;
Le mibuzo ibuyisa inani lemiqolo etafileni. Kulo mzekelo, u-7.
Ukubala iimilinganiselo eziyingqayizivele kwiKholamu
Ungasebenzisa kwakhona umsebenzi we-COUNT ukuchonga inani leempawu ezizodwa kwikholam. Kulo mzekelo, ukuba ufuna ukufumanisa inani labathengisi abahlukeneyo abaneemveliso zabo ezivela kwisebe lemveliso, unokukwazi ukufeza oku ngokusebenzisa umbuzo olandelayo:
UKUKHETHA COUNT (UMSEBENZI WOMSEBENZI)
UMTHETHO;
Lo mbuzo ubuyisela inani leempawu ezihlukileyo ezifumaneka kwikholam yeNgcaciso. Kule meko, impendulo i-3, emele 1, 2, no-3.
Ukubalwa kweeRekhodi zokuBaluleka kweeRekhodi
Hlanganisa nomsebenzi we-COUNT () kunye neCANDELO le-WHERE ukuchonga inani lamarekhodi ahambelana nemigangatho ethile. Ngokomzekelo, cinga ukuba umphathi weSebe ufuna ukufumana umgangatho wezinga lempahla kwisebe. Umbuzo olandelayo ukhankanya inani lemiqolo emele i-UnitsIntock ngaphandle kweeyunithi ezingama-50:
HLOLA COUNT (*)
UMTHETHO
LAPHO UnitsIntock <50;
Kule meko, umbuzo wawuza kubuyisa ixabiso le-4, emele i-Chai, i-Chang, iSyreded Syrup kunye no-Uncle Bob's Organic Pears Pears.
Isigatshana esingu-COUNT () sinokubaluleka kakhulu kubalawuli beenkcukacha abafuna ukufingqa idatha ukuze bahlangabezane neemfuno zoshishino. Ngobuchule obuncinane, ungasebenzisa umsebenzi we-COUNT () ngeenjongo ezahlukeneyo.