table-relationships

问题 I am very new to both Android development & Azure Mobile Services. I have a decent knowledge of Java so Android development is not proving to be too difficult. Although, I am struggling to gain a good knowledge of working with Azure Mobile Services. I have little knowledge of REST API's but will be able to learn quite quickly if required. My main concerns/questions are as followed: Can I build my Android app by using Mobile Services Data & API's alone. i.e the simple table values and the

问题 I am very new to both Android development & Azure Mobile Services. I have a decent knowledge of Java so Android development is not proving to be too difficult. Although, I am struggling to gain a good knowledge of working with Azure Mobile Services. I have little knowledge of REST API's but will be able to learn quite quickly if required. My main concerns/questions are as followed: Can I build my Android app by using Mobile Services Data & API's alone. i.e the simple table values and the

问题 Please help me! Im creating a database to store data about patients in an A&E Department. However, Im unsure how to relate the tables. Table structure: PATIENTS (PatientID(PK),Forename, surname, gender, DOB, Address, History, illness, priority) A&E (ID(PK), PatientID(FK), address, city, postcode, telenumber) NURSE (NurseID(PK), forename, surname) CONDITION (ID(PK), PatientID(FK) symptoms, diagnosis, treatment) Basically the relationships between these are: PATIENT attends A&E PATIENT seen_by

问题 I have three models that I want to interact with each other. Kase, Person and and Company. I have (I think) setup the relationships correctly: class Kase < ActiveRecord::Base #HAS ONE COMPANY has_one :company #HAS MANY PERSONS has_many :persons class Person < ActiveRecord::Base belongs_to :company class Company < ActiveRecord::Base has_many :persons def to_s; companyname; end I have put the select field on the create new Kase view, and the create new Person view as follows: <li>Company<span><

问题 I have read numerous thread on the above question, but none of the answers satisfy the problem. My problem is two tables that are linked to each other (in a one to one relationship) using an "ID" field which is also the primary key. When I try to enter a record in the the main table (Don't know if Access knows this is the main table) the I get the following error: "You cannot add or change a record because a related record is required in table" Could anyone please help me with this? Thanks

问题 I just finished the Michael Hartl Rails Tutorial. Trying to make something of my own. I am having trouble with getting rails to understand the relationships I'm trying to create. I'll try to simplify this as much as possible. A tree with branches, twigs and leaves would be apt, but... I'll use the parent child format as an example. So naturally I have users, and let's say users create families. So: Class User < ActiveRecord::Base has_many :families has_many :parents has_many :children end

问题 does setting up proper relationships in a database help with anything else other than data integrity? do they improve or hinder performance? 回答1: I'd have to say that proper relationships will help people to understand the data (or the intention of the data) better than if omitting them, especially as the overall cost is quite low in maintaining them. Their presence doesn't hinder performance except in terms of architecture (as others have pointed out, data integrity will occasionally cause

问题 Is it possible to compute an aggregation (ex.: sum) of an expression (ex.: subtraction) of fields from a related table in a Django ORM query? For a full example of what I'm trying to achieve, see this working SQL Fiddle. I broke it down into two questions (other one here). In this case, I have a model Sequence that represents a sequence of numbers, and a model Part that represent a "link" in this sequence: Sequence Sequence Sequence Sequence ... 0 5 20 15 ... |-- Part --|-- Part --|-- Part --

问题 I have a one-to-one relationship between an SLD table and an ORDER table. The SLD table is the main form, ORDER table is the subform. The main form's table has more records than the subform table. Master and child links are set. I have decompiled and have done compact and repair. I suspect my application is malfunctioning. In that case it is not the first time (I have fixed it before). Nothing seems to be working this time. I have also imported into a new database. On form-load both forms and

问题 Please help me understand further the many to many relationship. Suppose I have Teacher and Students Table and in my understanding it is one-to- many . Teacher TeacherId Primary Key TeacherName Student StudentId Primary Key TeacherId Foreign Key StudentName TeacherId can appear several times in the Student Table. I'm confused because Student can have many teacher. When can I say something is one-to-many and when is it many to many ? I can say One Student can have many teacher. On the other