Cov txheej txheem:
Video: Yuav ua li cas kuv tso ib qho kev txwv hauv SQL?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Lub SQL syntax tshem tawm qhov txwv los ntawm lub rooj yog,
- ALTER TABLE "table_name" DROP [ CONSTRAINT |INDEX] "CONSTRAINT_NAME";
- ALTER TABLE Customer DROP INDEX Con_First;
- ALTER TABLE Customer DROP CONSTRAINT Con_First;
- ALTER TABLE Customer DROP CONSTRAINT Con_First;
Raws li, yuav ua li cas ntxiv thiab tshem tawm cov kev txwv hauv SQL?
Rau ntxiv ib tug tshwj xeeb los yog lub ntsiab tseem ceeb, ib tug referential txwv , los yog check txwv , siv cov Tsim TABLE los yog ALTER TABLE nqe lus. Rau tshem tawm a txwv , siv ALTER TABLE nqe lus. Txhawm rau ua kom tus yuam sij no yog tus yuam sij tshwj xeeb, hloov lo lus tseem ceeb PRIMARY nrog UNIQUE.
Ib tug kuj yuav nug, koj yuav hloov cov kev txwv hauv SQL li cas? Siv SQL Server Management Studio
- Hauv Object Explorer, right-click lub rooj uas muaj cov kev txwv kos thiab xaiv Tsim.
- Nyob rau ntawm Table Designer ntawv qhia zaub mov, nyem Kos Cov Kev Txwv.
- Nyob rau hauv Cheeb Tsam Constraints dialog box, nyob rau hauv Selected Check Constraint, xaiv qhov txwv koj xav hloov.
Tom qab ntawd, lo lus nug yog, koj tuaj yeem tshem tawm qhov kev txwv?
Tshem tawm qhov txwv . Koj tuaj yeem yooj yim tshem tawm ib qho kev txwv los ntawm ob npaug rau nyem rau ntawm txoj haujlwm> cov ntaub ntawv ua haujlwm> qib siab> txwv ntaus > sai li sai tau.
Peb puas tuaj yeem tso tseg qhov kev txwv tseem ceeb?
Muab Cov Ntsiab Tseem Ceeb Tso Rau Koj ua tsis tau poob a thawj qhov tseem ceeb txwv yog lwm lub rooj muaj txawv teb chaws qhov tseem ceeb txwv uas references thawj tus yuam sij . Rau poob tus thawj tus yuam sij , koj yuav tsum xub poob tag nrho txawv teb chaws cov yuam sij uas siv nws.
Pom zoo:
Puas muaj ib txoj hauv kev hauv IAM system tso cai lossis tsis kam nkag mus rau ib qho piv txwv tshwj xeeb?
Tsis muaj txoj hauv kev hauv IAM system tso cai lossis tsis kam nkag mus rau kev ua haujlwm ntawm ib qho piv txwv tshwj xeeb. IAM tso cai rau kev nkag mus rau cov piv txwv tshwj xeeb
Yuav ua li cas koj tso ib qho kev txwv tshwj xeeb hauv Oracle?
Cov syntax rau tso tseg ib qho kev txwv tshwj xeeb hauv Oracle yog: ALTER TABLE table_name DROP CONSTRAINT constraint_name; table_npe. Lub npe ntawm lub rooj hloov
Dab tsi yog qhov kev txwv kev ncaj ncees piav qhia txog kev ncaj ncees lossis kev txwv txawv teb chaws?
Kev lees paub ncaj ncees xav kom tus yuam sij txawv teb chaws yuav tsum muaj tus yuam sij tseem ceeb sib xws lossis nws yuav tsum yog null. Qhov kev txwv no tau teev tseg ntawm ob lub rooj (niam txiv thiab menyuam); nws tuav cov ntawv xov xwm ntawm kab hauv cov rooj no. Nws txhais tau hais tias kev siv los ntawm kab hauv ib lub rooj mus rau lwm lub rooj yuav tsum siv tau
Yuav ua li cas koj tso ib qho kev txwv hauv db2?
Cov txheej txheem Kom meej meej tso tseg cov kev txwv tshwj xeeb, siv DROP UNIQUE clause ntawm ALTER TABLE nqe lus. Txhawm rau tso cov kev txwv tseem ceeb, siv DROP PRIMARY KEY clause ntawm ALTER TABLE nqe lus. Txhawm rau tso (table) xyuas cov kev txwv, siv DROP CHECK clause ntawm ALTER TABLE nqe lus
Kuv yuav txwv tsis pub muaj kev faib tawm ntawm ib qho khoom hauv C ++ li cas?
Stack raws li cov khoom yog implicitly tswj los ntawm C ++ compiler. Lawv raug rhuav tshem thaum lawv tawm ntawm qhov kev txwv thiab cov khoom siv dynamically faib yuav tsum tau muab tso tawm manually, siv tus neeg teb xov tooj tshem tawm txwv tsis pub lub cim xeeb xau tshwm sim. C ++ tsis txhawb nqa cov khib nyiab tsis siv neeg siv los ntawm cov lus xws li Java & C #