Sebelisa SQL COUNT ho khutlisa boitsebiso bo bongata bo fapaneng
Karolo ea lipotso ke karolo ea bohlokoa ea Sebopeho sa Lipotso (Structured Query Language) (SQL). E fumana lintlha tse thehiloeng ho lits'ebetso tse khethehileng ho tloha lefapheng la basebetsi. U ka sebelisa lipotso tsa SQL - ho kenyeletsa mosebetsi oa COUNT () - ho fumana boitsebiso ba mefuta eohle boitsebisong.
Mosebetsi oa SQL COUNT () o sebetsa ka ho khetheha hobane o nolofalletsa ho bala litlaleho tsa basebetsi tse thehiloeng ho lits'ebetso tse khethiloeng ke moetsi. U ka e sebelisa ho bala litlaleho tsohle tafoleng, ho bala litekanyetso tse ikhethang ka har'a kholumo, kapa ho bala palo ea linako tse tlaleha litlaleho tse finyellang maemo a itseng.
Sehlooho sena se sheba ka bokhutšoanyane se seng le se seng sa liketsahalo tsena.
Mehlala ena e thehiloe ho database e sebelisoang hangata ea Northwind, e atisang ho tsamaisoa ka lihlahisoa tsa ditshwantsho bakeng sa ho sebediswa e le thupelo.
Mona ke karolo e hlahang ho tsoa tafoleng ea Lihlahisoa tsa Meralo:
| ProductID | ProductName | SupplierID | PaloPerUnit | Theko ea thepa ka 'ngoe | UnitsIntock |
|---|---|---|---|---|---|
| 1 | Chai | 1 | Mabokoseng a 10 x mekotla e 20 | 18.00 | 39 |
| 2 | Phetoho | 1 | Li-bottle tse 24 - 12 oz | 19.00 | 17 |
| 3 | Syrup e nang le anise | 1 | Li-bottle tse 12 - 550 ml | 10.00 | 13 |
| 4 | Cajun Season Chef ea Chef | 2 | 48 - 6 litsu tse 6 | 22.00 | 53 |
| 5 | Mofuthu oa Anton oa Gumbo | 2 | Mabokose a 36 | 21.35 | 0 |
| 6 | Nkhono oa Boysenberry oa Hasana | 3 | 12 - 8 oz linkho | 25.00 | 120 |
| 7 | Malome Bob's Organic Pears a omisitsoeng | 3 | 12 - 1 lb pkgs. | 30.00 | 15 |
Ho bala Litlaleho ka Letlapa
Potso ea motheo ka ho fetisisa ke ho bala palo ea litlaleho tse tafoleng. Haeba o batla ho tseba palo ea lintho tse teng tafoleng ea lihlahisoa, sebelisa potso e latelang:
KHETHA COUNT (*)
HO tsoa sehlahisoa;
Potso ena e khutlisa palo ea mela e tafoleng. Mohlala ona, o 7.
Ho bala Melao e ikhethang ka Khoeli
U ka boela ua sebelisa mesebetsi ea COUNT ho khetholla palo ea litekanyetso tse ikhethang ka kholeng. Mohlala, haeba u batla ho khetholla palo ea bafani ba fapaneng bao lihlahisoa tsa bona li hlahang lefapheng la lihlahisoa, u ka finyella sena ho sebelisa potso e latelang:
Khetha SETSOLELE (DISTINCT SupplierID)
HO tsoa sehlahisoa;
Potso ena e khutlisa palo ea litekanyetso tse fapaneng tse fumanoang khoeling ea SupplierID. Tabeng ena, karabo ke 3, e emelang 1, 2, le 3.
Ho bala Litlaleho tsa Boikokobetso
Kopanya mosebetsi oa COUNT () le sepheo sa WHERE ho khetholla lenane la litlaleho tse lumellanang le litekanyetso tse itseng. Ka mohlala, re re mookameli oa lefapha o batla ho utloisisa maemo a lichelete lefapheng lena. Potso e latelang e khetholla palo ea mela e emelang UnitsIntock ntle le litekanyetso tse 50:
KHETHA COUNT (*)
HO tsoa sehlahisoa
MOKHOA OA LINTHOAA <50;
Tabeng ena, potso ena e ne e tla khutlisa bohlokoa ba 4, e emelang Chai, Chang, Aniseed Syrup le Pear Bob's Organic Pears Pears.
Mantsoe a COUNT () a ka ba a bohlokoa haholo ho basebelisi ba ditshwantsho ba batlang ho akaretsa dintlha ho finyella ditlhoko tsa khoebo. Ka bokhoni bo fokolang, u ka sebelisa karolo ea COUNT () bakeng sa mefuta e sa tšoaneng.