I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition. Null by defi...
百度试题 结果1 题目Which constraint can be defines only at the column level? ()A. UNIQUE B. NOT NULL C. ECK D. PRIMARY KEY E. FOREIGN KEY相关知识点: 试题来源: 解析 A 反馈 收藏
I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition. Null by defi...
百度试题 结果1 题目Which constraint can be defines only at the column level? ()UNIQUEB、 NOT NULLCHECKPRIMARY KEYFOREIGN KEY 相关知识点: 试题来源: 解析 B 反馈 收藏
Minimize unique parts It's bad enough to use dozens of parts when a few lines of code would do. What's worse is to have dozens of one-of-a-kind, custom, handmade, imported, or otherwise nonstandard parts. Ever tried putting together a tent with four different lengths of poles and sev...
This point of view may actually be much more deeply rooted in the minds of overseas Chinese. They have complained that the use of the term Waiguoren to describe them hurts their feelings, as they worked hard for the construction of China even when they were in a foreign county. This ...
How to make FOREIGN KEY and allow to have 0 value how to make sure for not empty XML element? How to make the Phone number in a regex pattern?? How To Make Unique Constraint Case Sensitive In SQL SERVER 2008? how to move table from one database to another database how to multiply...
40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */; /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */; /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */; -- -- Create schema test -- CREATE DATABASE...
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I think it's related to the constraint name not being unique, could you try... ALTERTABLE`NotificationUserIssuedCard`ADDCONSTRAINTNotificationUserIssuedCard_userId_fkFOREIGN KEY(`userId`)REFERENCES`User`(`id`); ? • edited Yep it works. ...