SQL jinsin, description, misalai, Properties

Sau da yawa idan ka yi amfani da SQL don dawo da bayanai daga Tables, mai amfani na'am da m data ne da wanzuwar wani cikakken m Kwafin layuka. Don kaucewa wannan halin da ake ciki, yin amfani da SQL jinsin shaida a jumla Zabi. Wannan labarin zai tattauna misalai na yin amfani da wannan shawara, kazalika da yanayi a cikin abin da aikace-aikace ya kamata a yi watsi da shawara.

Kafin mu fara mu shawara na musamman misalai, haifar da database ake bukata kamar wata Tables.

shirye-shiryen tebur

Tunanin cewa muna da database Stores bayani game da fuskar bangon waya gabatar a alluna biyu. Wannan tebur oboi (wallpaper) zuwa id filayen (farɗan mai ganowa), na da irin (irin wallpaper -. Takarda, roba, da sauransu), launi (launi), a struct (tsarin) da kuma farashin (da farashin). Kuma tebur Ostatki (sharan) tare da id_oboi filayen (a tunani da farɗan mai ganowa a tebur Oboi) da kuma count (yawan Rolls a stock).

Cika da data tebur. A tebur ƙara fuskar bangon waya 9 records:

A tebur da ragowar - da tara records:

Mu ci gaba da bayanin irin jinsin domin a SQL.

Wajen da jinsin a cikin Zabi magana

jinsin shawara ya kamata a sanya nan da nan bayan da Zaži keyword a queries. Ya shafi duk ginshikan kayyade a cikin jumla Zabi, domin shi za a cire daga karshe tambaya sakamakon da cikakken m kirtani. Saboda haka, sau ɗaya isa zuwa saka lokacin rubuta SQL «zaži jinsin» request. A togiya ne yin amfani da jinsin ciki tara ayyuka da cewa kalle kadan baya.

Ya kamata a tuna cewa mafi database da kuma ba ya gane your irin request:

Akwai aka gani ba, da ya kasance hujjarsu sau da yawa, ko da sau daya a kayyade ba, amma kafin na biyu, uku ko wani zabi shafi. Za ka samu wani kuskure nufin wani kuskure a cakude.

Aikace-aikace jinsin queries a misali

Babu shakka cewa da ta dace gini tsarin alluna da ciko su a cikin guda tebur cire halin da ake ciki a lokacin da akwai cikakken m kirtani. Saboda haka, tambaya kisa «Zabi jinsin *» tare da wani samfuri na daya tebur ne impractical.

Ka yi la'akari da halin da ake ciki a lokacin da muke bukatar mu san abin da irin da muke da fuskar bangon waya, kawai don saukaka, don warware ta irin:

Kuma samun sakamakon:

Kamar gani a teburin akwai Kwafin layuka. Idan muka ƙara da shawara Zabi jinsin:

mun samu sakamakon ba tare da maimaitawa:

Saboda haka, idan yadda ya kamata shigar data a wani tebur, sa'an nan nan da nan bayan wata wayar kira ko request na saye mu iya amsa da cewa ruwa wallpaper, fiberglass da acrylic wallpaper samuwa a cikin kantin sayar da ba. Ganin cewa kewayon shagunan da aka yawanci ba a iyakance ba zuwa ɗaya da ɗari wallpaper, duba jerin wadanda ba musamman iri zai zama quite aiki-m.

Aikace-aikace na jinsin tara ayyuka a cikin

SQL jinsin shawara za a iya amfani da wani tara aiki. Amma ga min da Max da aikace-aikace zai yi wani tasiri ba, amma a lokacin da kirga Naira Miliyan Xari ko da talakawan darajar ne da wuya a halin da ake ciki inda ba wanda zai yi la'akari da maimaitawar.

Misali muna so mu duba damar mu sito, kuma ka aika da wannan bukatar, computes jimlar yawan coils a stock:

Request zai ba da amsar 143. Idan, duk da haka, mu canza to:

mun samu jimlar 119, azaman fuskar bangon waya ga wani ɓangare lambobi 3 da kuma 7 ne a stock a cikin wannan adadin. Amma shi ne bayyananne cewa amsar ba daidai ba ne.

Mafi sau da yawa amfani da SQL jinsin aiki Count. Saboda haka, za mu iya gano yadda da yawa musamman iri wallpaper, ba mu da:

Kuma samun sakamakon of 5 - talakawa takarda da biyu-Layer roba da kuma wadanda ba saka masana'anta. Lalle ne, duk gani da tallace da kamar: "Kawai muna da sama da 20 daban-daban na wallpaper," ta wanda yake nufi da cewa wannan kanti ba kawai kamar wata da dozin Rolls kuma da dama wallpaper zamani iri.

Yana da ban sha'awa cewa a wannan tambaya, ba za ka iya saka mahara ayyuka kamar Count sanyã jinsin, da kuma ba tare da shi. Wannan shine kadai halin da ake ciki inda jinsin a Select'e iya zama ba sau da dama.

Lokacin da ta yi watsi da amfani da shawara

Daga cikin yin amfani da SQL jinsin shawara ya kamata a yi watsi da a daya daga biyu lokuta:

1. Ka yi mai selection na alluna da suke m, a cikin na musamman darajar kowane. A wannan yanayin, da amfani da shawara ne da bai dace ba, saboda yana da wani ƙarin kaya a kan uwar garke, ko abokin ciniki (dangane da irin DBMS).
2. Shin, kuna tsoron rasa your data. Bari mu bayyana.

Tsammani Kocin tambaye ka ka lissafa abubuwan da fuskar bangon waya cewa kana da, tare da nuni da kawai biyu ginshikan - da irin da kuma launi. Daga al'ada, ku bayar da wani misãli ba jinsin:

Kuma - rasa wasu bayanan:

Yana iya ba da alama cewa takardar wallpaper (na al'ada da kuma dual-Layer) muka daya kawai tuna, a gaskiya har cikin kananan tebur na biyu labarin (haifar ba tare da jinsin):

Saboda haka, kamar yadda a cikin rubutu da wani request da shawara jinsin bukatar ka mai da hankali da kuma m yanke shawara a kan ta aikace-aikace, dangane da aiki.

madadin jinsin

Saba wa shaida jinsin - All shawara. A aikace Kwafin layuka an adana. Amma a matsayin tsoho database da kuma gano cewa, wajibi ne a nuna duk dabi'u, da ya kasance hujjarsu All - shi ne wajen wani share fage na gasar fiye da ainihin aikin shawara. Muna fatan cewa ka yanzu fahimci cewa jinsin (SQL) da ake amfani. Description ba ka cikakken bayani game da yiwuwa na amfani da wannan shawara a warware daban-daban matsaloli. Bayan duk, kamar yadda ya juya waje, har irin wannan sauki shaida a aikace boyewa sosai ri yiwuwar rasa wasu bayanai da kuma nuna m bayani.