Shandisa SQL COUNT kuti adzokere zvakasiyana-siyana zve data
Icho chinhu chinokosha chikamu chinokosha cheStructured Query Language (SQL). Inotora dheti zvichienderana nematauriro chaiwo kubva kune dhesi rezvekodzero. Iwe unogona kushandisa SQL mibvunzo - kusanganisira COUNT () basa - kuwana mamwe marudzi ehuwandu kubva kune database.
SQL COUNT () basa rinonyanya kukosha nokuti inokubvumira kuti uverenge zvinyorwa zvemashoko ezvinyorwa zvichienderana nemitemo-yakatsanangurwa. Iwe unogona kuishandisa kuti uverenge zvese zvinyorwa zviri patafura, uverenge humwe hutsika huri muhwendefa, kana kuverenga nhamba yezvinyorwa zvinyorwa zvinoitika zvinosangana nezvimwe zviyero.
Nyaya iyi inotarisa muchidimbu chimwe nechimwe chezviitiko izvi.
Mienzaniso yacho inobva pane dhiyabhorosi inowanzoshandiswa, iyo inowanzoendeswa nemigodhi yemagadziro ekushandisa sekudzidzisa.
Heino zvakanyanyiswa kubva pane dheti yeMichafura yemuchina:
| ProductID | ProductName | SupplierID | QuantityPerUnit | UnitPrice | UnitsIntock |
|---|---|---|---|---|---|
| 1 | Chai | 1 | 10 mabhokisi x 20 mabhegi | 18.00 | 39 |
| 2 | Chang | 1 | 24 - 12 oz mabhodhoro | 19.00 | 17 |
| 3 | Aniseed Syrup | 1 | 12 - 550 ml mabhodhoro | 10.00 | 13 |
| 4 | Chef Anton's Cajun Mwaka | 2 | 48 - 6 oz jars | 22.00 | 53 |
| 5 | Chef Anton's Gumbo Mix | 2 | 36 mabhokisi | 21.35 | 0 |
| 6 | Ambuya va Boysenberry Vanoparadzira | 3 | 12 - 8 oz jars | 25.00 | 120 |
| 7 | Uncle Bob's Organic Akaoma Pears | 3 | 12 - 1 lb pkgs. | 30.00 | 15 |
Kuverenga Zvinyorwa muTereta
Chidzidzo chekutanga chinonzi kuverenga nhamba yezvinyorwa zviri patafura. Kana iwe uchida kuziva nhamba yezvinhu zviripo mune tafura yezvigadzirwa, shandisa mhinduro inotevera:
Sarudza COUNT (*)
FROM chibereko;
Uyu mubvunzo unodzorera nhamba yemitsara iri patafura. Mumuenzaniso uyu, iri 7.
Kuverenga Maitiro Akasiyana-siyana muColumn
Iwe unogonawo kushandisa COUNT basa kuti uone nhamba yezvinhu zvakasiyana-siyana mumutsetse. Mumuenzaniso, kana iwe uchida kuziva nhamba yevatengesi vakasiyana-siyana vane michina inowanikwa mune dhipatimendi rekugadzira, unogona kuita izvi uchishandisa mubvunzo unotevera:
Sarudza COUNT (DISTINCT SupplierID)
FROM chibereko;
Uyu mubvunzo unodzorera huwandu hwehutsika hwakasiyana hunowanikwa mumutsetse we SupplierID. Muchiitiko ichi, mhinduro ndeyechitatu, inomiririra 1, 2, uye 3.
Kuverenga Dhiyabhorosi Matanho ekufananidza
Gadzirai COUNT () basa neQUERE WHERE kuti uone nhamba yezvinyorwa zvinofanana nezvimwe zviyero. Somuenzaniso, funga kuti maneja wehurumende anoda kuti awane pfungwa yehuwandu hwezvikwata mubazi. Tsva inotevera inoratidza nhamba yemitsetse inomiririra UnitsIntock kunze kwemasuniti makumi mashanu:
Sarudza COUNT (*)
FROM chibereko
WHERE UnitsIntock <50;
Muchiitiko ichi, mhinduro yacho inogona kudzorera kukosha kwe4, iyo inomiririra Chai, Chang, Aniseed Syrup, uye Uncle Bob's Organic Dried Pears.
Gwaro re COUNT () rinogona kuva rakakosha kune vatariri vepa database vanoedza kupfupisa deta kuti vawane zvido zvebhizimisi. Nekugadzirisa zvishoma, unogona kushandisa COUNT () basa kune zvakasiyana-siyana zvinangwa.