foreign-keys

问题 I'd like to ask regarding a particular issue I have. For example, I have a Student table that has a SchoolID and a ClassID , both of which are foreign keys to the School and Classroom tables respectively. The Class table has a SchoolID column which is a foreign key to the School table. Is there any way I can ensure that the ClassID in the Student table is a child of the SchoolID , or must I remove the SchoolID and just live with the ClassID in order to prevent any possible discrepancies? 回答1:

问题 I have the following 3 tables: tblA ID - PK name tblB ID - PK tblAID - FK references tblA.ID pkID2 tblC ID - PK tblAID * fkID2 * ... I want to make this tuple a FK of (tblB.tblAID, tblB.pkID2) If I do this: alter table tblC with check add constraint FK_tblC_tblB foreign key (tblAID, fkID2) references tblB (tblAID, pkID2) I get an error message: There are no primary or candidate keys in the referenced table 'tblB' that match the referencing column list in the foreign key 'FK_tblC_tblB' I.e.: I

问题 When creating many to many relationships we use an intermediary table. Lets say I use the following entities video , category , tag , and VideoCategory , VideoTag to create the relations. I'm assuming that many tags/categories can have many videos and vice-versa. And I do it with through keyword 'cause I want to be able to use extra fields in the future if I want. class Category(models.Model): category = models.CharField(max_length=50) def __str__(self): return self.category class Tag(models

问题 There always be the error: "Cannot add foreign key constraint" when I create my last table . System: Mac OS X 10.9 DB : MySQL 5.6.14 DBM : Sequel Pro CREATE TABLE users ( uid INT AUTO_INCREMENT PRIMARY KEY, uname VARCHAR(20) NOT NULL, uemail VARCHAR(20) NOT NULL, ucity VARCHAR(20), upassw VARCHAR(20) NOT NULL ); CREATE TABLE songs( sid INT AUTO_INCREMENT PRIMARY KEY, sname VARCHAR(20) NOT NULL, srldate DATE NOT NULL ); CREATE TABLE albums ( albid INT AUTO_INCREMENT PRIMARY KEY, albname

问题 In Loopback how can I create tags? For example there are projects { id, name } and there are tags collection with the similar model Now the project needs to have multiple tags, and the same tag can be used in multiple projects. For example while creating a project, the user may type already existing tags, or new tags, and those should be added to the project. I can't find the exact relationship I need in the loopback framework. How do you do that? 回答1: TLDR CREATE TABLE ProjectTag (id AUTO

问题 In laravel, I have 3 table User // for Authentication and Create Another User Once logged in Expense Shop My Purpose- I want user can register and Also, can create another user when they logged in And Can assign user to another Shop as they want.. And Only User in the Same Shop Can see their Expense .. // My User Table <pre> Schema::create('users', function (Blueprint $table) { $table->bigIncrements('id'); $table->unsignedBigInteger('shop_id')->nullable(); $table->unsignedBigInteger('user_id'

问题 I'd like to get all the Foreign Key columns in a Table in my entity. For example: class User { Id {get;set;} Name {get;set;} ColumnWithForeignKey1Id{get;set;} ColumnWithForeignKey2Id{get;set;} ColumnWithForeignKey3Id{get;set;} } result should be like: ColumnWithForeignKey1Id ColumnWithForeignKey2Id ColumnWithForeignKey3Id 回答1: Open your dbml file in an xml editor and you'll see foreign keys: <Association Name="Table1_Table2" Member="Table1" ThisKey="Table2ID" OtherKey="ID" Type="Table2"

问题 I Tried a few options to generate DDL from oracle database using SQL Developer and none of them fit the purpose. The Quick DDL option results in DDL without Foreign Key constraints. I do like the format The Edit on table results in DDL including storage and loggings which I cannot get rid of. Just wondering anyone have better way of generating DDL using SQL Developer? Thanks 回答1: The Quick DDL doesn't use any sort of preferences, it does it by what we think is appropriate - which is totally

问题 mysql> create table products(id integer unsigned auto_increment primary key); Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE orders ( -> id integer PRIMARY KEY auto_increment, -> product_id integer REFERENCES products (id), -> quantity integer, -> INDEX product_id_idx (product_id) -> ); Query OK, 0 rows affected (0.05 sec) mysql> insert into orders(product_id,quantity) value(1,1); Query OK, 1 row affected (0.00 sec) Since product 1 doesn't exist,the insert statement is supposed to

问题 mysql> create table products(id integer unsigned auto_increment primary key); Query OK, 0 rows affected (0.05 sec) mysql> CREATE TABLE orders ( -> id integer PRIMARY KEY auto_increment, -> product_id integer REFERENCES products (id), -> quantity integer, -> INDEX product_id_idx (product_id) -> ); Query OK, 0 rows affected (0.05 sec) mysql> insert into orders(product_id,quantity) value(1,1); Query OK, 1 row affected (0.00 sec) Since product 1 doesn't exist,the insert statement is supposed to