Kusankha Dongosolo M'kati mwa SQL

Kufotokozera PATSAMBA WHERE ndi PAKATI PA chikhalidwe

Language Structured Query (SQL) imapereka mwayi wosankha anthu omwe akugwiritsa ntchito database kuti adziwe mauthenga omwe angakonzedwe kuti achoke pamabuku. M'nkhani yam'mbuyomu, tafufuza zochotsa mauthenga kuchokera ku databata pogwiritsa ntchito mafunso a SQL SELECT . Tiyeni tiwonjeze pa zokambiranazi ndikufufuze momwe mungapangire mafunso apamwamba kuti mutenge deta yomwe ikugwirizana ndi zikhalidwe zina.

Tiyeni tikambirane chitsanzo chokhazikika pogwiritsa ntchito nsanja ya Northwind yomwe imagwiritsidwa ntchito nthawi zambiri.

Pano pali ndondomeko yochokera ku ndondomeko ya Masitolo:

Mndandanda wa Zamalonda

ProductID	Zamalonda	SupplierID	ChiwerengeroPerUnit	Mtengo wagawo	UnitsIntock
1	Chai	1	Mabokosi 10 x matumba 20	18.00	39
2	Kusintha	1	24 - 12 oz mabotolo	19.00	17
3	Sirave Yowoneka	1	12 - 550 ml mabotolo	10.00	13
4	Mtsinje wa Anton wa Cajun Seasoning	2	48 - 6 oz mitsuko	22.00	53
5	Gumbo Mix ya Chef Anton	2	36 mabokosi	21.35	0
6	Agogo a Boysenberry Akufalikira	3	12 - 8 oz mitsuko	25.00	120
7	Amalonda a Amal Bob's Peanic Zouma	3	12 - 1 lb pkgs.	30.00	15

Zinthu Zosavuta Kwambiri

Zolembedwa zoyamba zomwe tidzayika pafunso lathu zimaphatikizapo malire osavuta. Tikhoza kufotokoza izi mu funso LAPERE la funso la SELECT, pogwiritsa ntchito mawu osavuta omwe amamangidwa ndi ogwira ntchito, monga <,>,> =, ndi <=.

Choyamba, tiyeni tiyese funso lophweka limene limatithandiza kuti tipeze mndandanda wa zinthu zonse zomwe zili mu database zomwe zili ndi UnitPrice yaposa 20.00:

SANKANI Zamtundu, Chinthu Chochokera KUZIKHALA ZIMENE UnitPrice> 20.00

Izi zikupanga mndandanda wa zinthu zinayi, monga momwe tawonetsera m'munsimu:

Mgwirizano wa Mgwirizano wa Mtengo ------- -------- Mphika wa Anton wa Gumbo Mix 21.35 Cajun Anton Cajun Nyengo 22.00 Agogo a Boysenberry Kufalikira 25.00 Amalume Bob's Peanic Zouma 30.00

Titha kugwiritsanso ntchito chiganizo cha WHERE ndi zoyendetsera chingwe. Izi mwachidule zimagwirizanitsa zilembo ndi manambala, ndi A akuimira mtengo 1 ndi Z akuimira mtengo 26. Mwachitsanzo, tikhoza kusonyeza malonda onse ndi mayina kuyambira ndi U, V, W, X, Y kapena Z ndi funso ili:

SANKANI Zamtundu WOTCHOKERA KUZIKHALIDWE MALO> = 'T'

Chimene chimapereka zotsatira:

Zamalonda ------- Peyala Bob's Organic Dry Pears

Kuwonetsera Mapu pogwiritsa ntchito Malire

Chigamulo cha WHERE chimatithandizanso kuti tigwiritse ntchito malingaliro osiyanasiyana pogwiritsa ntchito zinthu zambiri. Mwachitsanzo, ngati tifuna kutenga funso lathu pamwamba ndi kuchepetsa zotsatira zogulitsa ndi mitengo pakati pa 15.00 ndi 20.00, tingagwiritse ntchito funso ili:

SANKANI Zamtundu, Chinthu Chochokera M'zinthu ZOTHANDIZA UnitPrice> 15.00 NDI UnitPrice <20.00

Izi zimapereka zotsatira zomwe zili pansipa:

Chigwirizano chaMtunduwuChigawo ------- -------- Chai 18.00 Kusintha 19.00

Kuwonetsera Mapangidwe PAKATI PA

SQL imaperekanso njira yochepetsera PAKATI PA syntax yomwe imachepetsa chiwerengero cha zinthu zomwe tifunikira kuziphatikiza ndikupangitsa kuti funsoli liwonekere. Mwachitsanzo, mmalo mogwiritsa ntchito zifukwa ziwiri zomwe zili pamwambapa, tikhoza kufotokoza zomwezo monga:

SANKANI Mtengo wa Zina, UnitPrice KUZIKHALA ZOKHALA PAMENE UnitPrice PAKATI PA 15.00 NDI 20.00

Monga momwe zilili ndi ziganizo zathu zina, PAKATI pogwira ntchito ndi zingwe zamtengo wapatali. Ngati tifuna kupanga mndandanda wa mayiko onse oyambira V, W kapena X, tingagwiritse ntchito funso:

SANKANI Zamtundu WOTCHOKERA KUZIKHALIDWE ZOCHITIKA PAKATI "A" ndi "D"

Chimene chimapereka zotsatira:

MtengoWake ------- Gulu la Antu's Chai Chang Chef Gumbo Anton's Cajun Seasoning

Chigamulo cha WHERE ndi gawo lamphamvu lachilankhulo cha SQL chomwe chimakulolani kuti mulepheretse zotsatira ku ziyeso zomwe zikugwera mndandanda. Zimagwiritsidwa ntchito kwambiri kuti zithandize kulingalira malingaliro a bizinesi ndipo ziyenera kukhala mbali ya chida chilichonse cha akatswiri a deta.

Nthawi zambiri zimakhala zothandiza kuphatikiza ndondomeko zomwe zimagwiritsidwa ntchito kuti zisungidwe kwa omwe alibe SQL chidziwitso.