Ho Khetha Ditaba kahare ho SQL

Ho hlahisa serapa sa WHERE le hara maemo

Puo ea Structured Query (SQL) e fa basebedisi ba ditshwantsho bokhoni ba ho etsa lipotso tse ikhethileng ho tlosa tlhahisoleseding ho tswa ho marang-rang. Sehloohong sa pejana, re ile ra hlahloba boitsebiso ba ho ntša boitsebiso bo tsoang ho database ho sebelisa lipotso tsa SQL SELECT . A re ke re atolose moqoqong oo 'me re hlahlobe hore na u ka etsa lipotso tse tsoetseng pele joang ho fumana lintlha tse lumellanang le maemo a itseng.

A re nahaneng ka mohlala o thehiloeng ho database ea Northwind e tloaelehileng e sebelisoang hangata e tsamaisoang ka lihlahisoa tsa ditshwantsho tsa thuto e le tutorial.

Mona ke karolo e hlahang ho tsoa tafoleng ea Lihlahisoa tsa Meralo:

Lethathamo la Sehlahiswa
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

Maemo a Boundary a Bonolo

Lithibelo tsa pele tseo re li behang lipotsong tsa rona li kenyeletsa maemo a bonolo. Re ka bonts'oa tsena lihlopha tsa WHERE tsa potso ea SELECT, ho sebelisa lipolelo tse bonolo feela tse entsoeng ka basebelisi ba tloaelehileng, tse kang <,>,> =, le <=.


Pele, a re lekang potso e bonolo e re lumellang hore re ntše lethathamo la lihlahisoa tsohle ho database e nang le UnitPrice ea fetang 20.00:

SELECT ProductName, UnitPrice HO LITHUTO TSE LENG UnitPrice> 20.00

Sena se hlahisa lenane la lihlahisoa tse 'nè, joalokaha ho bontšitsoe ka tlase:

ProductName UnitPrice ------- -------- Sefate sa Anton's Gumbo Mix 21.35 Cajun Chef ea Cajun Nako ea 22.00 Bo-'mè ba Boysenberry Ho Ajoa 25.00 Malome Bob oa Pears a omisitsoeng 30.00

Re ka boela ra sebelisa polelo ea WHERE e nang le lithane tsa khoele. Ha e le hantle, re ka bontša lihlahisoa tsohle ka mabitso ho qala ka U, V, W, X, Y kapa Z ka lipotso tse latelang:

Khetha Ntho e Ncha HO LITHUTO TSE LENG Tlhahlobo> = 'T'

E hlahisang phello:

ProductName ------- Lipalesa tsa Malome Bob's Organic tse omisitsoeng

Ho hlalosa mekhoa e sebelisang meeli

Sehlopha sa WHERE se boetse se re lumella ho kenya ts'ebetso ea boemo bo bongata ka boleng ka ho sebelisa maemo a mangata. Ka mohlala, haeba re batla ho nka potso ea rona ka holimo ebe re fokotsa liphello ho lihlahisoa le theko pakeng tsa 15.00 le 20.00, re ka sebelisa potso e latelang:

SELECT ProductName, UnitPrice HO LITHUTO TSE LENG UnitPrice> 15.00 LE UnitPrice <20.00

Sena se hlahisa sephetho se bontšitsoeng ka tlase:

ProductName UnitPrice ------- -------- Chai 18.00 Phetoho 19.00

Ho bontša mekhahlelo ka nako e lekaneng

SQL e boetse e fana ka tsela e khutšoanyane ho tloha nakong ea syntax e fokotsang palo ea maemo ao re lokelang ho a kenyelletsa le ho etsa hore potso e khonehe haholoanyane. Ka mohlala, ho e-na le ho sebelisa maemo a mabeli a HLAHANG ka holimo, re ka hlalosa potso e tšoanang le e latelang:

SELECT ProductName, UnitPrice HO LITHUTO TSE LENG UnitPrice ho tloha 15.00 LE 20.00

Joaloka lihlopha tse ling tsa maemo a rona, NAKONG ea ho sebetsa ka thoko le litekanyetso. Haeba re batla ho hlahisa lethathamo la linaha tsohle tse qala ka V, W kapa X, re ka sebelisa potso ena:

Khetha Ntho e Ncha HO LITHUTO TSE LENG NTHO E NENG PELE KA "A" le "D"

E hlahisang phello:

ProductName ------- Li-aniseed Syrup Chai Chang Chef Li-Anton's Gumbo Mix Ka lebaka la Chef Anton's Cajun Seasoning

Sepheo sa WHERE ke karolo e matla ea puo ea SQL e lumellang hore u thibele liphetho ho litekanyetso tse oelang ka har'a mararo a hlalositsoeng. Ho tloaelehile ho sebelisoa ho thusa ho hlalosa lintlha tsa khoebo 'me e lokela ho ba karolo ea sesebelisoa sa lithulusi tsa setsebi se seng le se seng.

Hangata hoa thusa ho kenngoa mekhahlelo e tloaelehileng ho kenngoa ts'ebetsong e boloketsoeng ho etsa hore e fumanehe ho ba se nang tsebo ea SQL.