Cov txheej txheem:
Video: Yuav ua li cas koj tso ib qho kev txwv hauv db2?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Txheej txheem
- Kom meej meej poob tshwj xeeb kev txwv , siv cov DROP UNIQUE clause ntawm ALTER TABLE nqe lus.
- Rau txo cov kev txwv tseem ceeb , siv cov DROP PRIMARY KEY clause ntawm ALTER TABLE nqe lus.
- Rau poob (rooj) check kev txwv , siv cov DROP CHECK clause ntawm ALTER TABLE nqe lus.
Ib yam li ntawd, kuv yuav ua li cas tso ib daim tshev txwv?
Lub syntax rau poob a xyuas qhov txwv hauv SQL Server (Transact-SQL) yog: ALTER TABLE table_name DROP CONSTRAINT constraint_name; table_npe. Lub npe ntawm lub rooj uas koj xav tau poob tus xyuas qhov txwv.
Ib tug kuj yuav nug, nqe lus twg yuav tso cai rau koj los cuam tshuam qhov kev txwv? ALTER TABLE hais kom ua nrog MODIFY clause tau siv los ua disable ib qho kev txwv.
Tib neeg kuj nug, peb puas tuaj yeem tshem tawm cov kev txwv hauv qhov tseem ceeb lossis txawv teb chaws?
Hauv qhov no koj tuaj yeem rho tawm thawj tus yuam sij ncaj qha. Yog tias txawv teb chaws key tsis yog thawj tus yuam sij nyob rau hauv lwm lub rooj rooj ces koj yuav tsum siv rau rho tawm cascade lus rau rho tawm tus thawj tus yuam sij . Cov lus ntawd yuav rho tawm tus yuam sij txawv teb chaws los ntawm ob lub rooj thiab ces rho tawm thawj tus yuam sij.
Dab tsi yog poob clause ntawm alter table?
DROP CONSTRAINT Clause . Siv cov DROP CONSTRAINT lus txhawm rau rhuav tshem qhov kev txwv uas twb muaj lawm uas nws lub npe koj teev. Qhov no syntax fragment yog ib feem ntawm ALTER TABLE nqe lus.
Pom zoo:
Yuav ua li cas kuv tso ib qho kev txwv hauv SQL?
SQL syntax kom tshem tawm qhov txwv tsis pub dhau 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;
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
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 #