relational

问题 This question is kind of a follow up to this question I asked a month ago. Here are my three tables. Fighters fighter_id | name ----------------------- 1 | John 2 | Steve 3 | Bill 4 | Bobby Events event_id | event_name | event_date ------------------------------------------- 1 | MMA | 01/01/2010 2 | Cool | 02/20/2010 3 | Yeaa! | 04/15/2010 Fights fight_id | fighter_a | fighter_b | winner | method | event ----------------------------------------------------------------------- 1 | 1 | 2 | 1 |

问题 This is part of a homework assignment. I've got several questions asking find the eid of the employee with the highest salary, or 2nd highest salary. Find the pilot that is certified for the most aircrafts. I don't have any idea on how to do it. There aren't any examples in the chapter, and google is proving less that helpful. If someone could show me how to do just one of these, it'll help a lot. here are the tables: Aircraft( aid : integer, aname : string, cruisingrange : integer )

问题 I have a middle tier containing several related objects and a data tier that is using a DataSet with several DataTables and relationships. I want to call a Save method on one of my objects (a parent object) and have its private variable data transformed into a DataRow and added to a DataTable. Some of the private variable data are actually other objects (child object) that each need to have their own Save method called and their own variable data persisted. How do I "lace" this together? What

问题 I'm trying to design a normalized relational database where a patient has a * contact person * (person who is contacted in case of emergency). I also have a table called contact_num which takes patient_id as a foreign key. But how can I implement having a emergency contact person (who has a phone number) who may/may not be another patient? Should I implement emergency_contact_num table? Or some kind of unary relationship? egs would be helpful 回答1: I think you could have a contacts book, all

问题 I have a question about relationships between two tables. Let's say we have a table users, and links. users +++++++++ id name 1 name1 2 name2 3 name3 +++++++++ links +++++++++ id link 1 link1 2 link1 3 link1 +++++++++ Now the normal way to link these two is with a name_links table. For example: name_links ++++++++++++ uid lid 1 1 1 3 2 3 2 1 2 2 3 2 ++++++++++++ Now i was wondering if it is a good idea to make a table like this name_links ++++++++++++ uid lid 1 1,3 2 1,2,3 3 2 ++++++++++++

问题 My data, IF it would be represented by objects, it would look like: abstract class A{ int a; int b; string c; } class B inherits A{ string D; } class C inherits A{ int e; int f; } My question: Do I create a separate table for entities B and C, Or do I create one main table, and for each entity type I do different joins to fetch the data. In the real world, I will have around 15 similar fields for all entities, and about 1-3 unique field for each entity. I expect a max of 100K records. Any

问题 I have the following data frame, call it DF, which is a data frame consisting in three vectors: "Chunk" "Name," and "Frequency." I need to turn it into a NameXName adjacency matrix where Names are considered adjacent when they reside in the same chunk. So for example, in the first lines, Gretel and Friedrich are adjacent because they are both in Chunk2. And the weight of the relationship should be based on "Frequency," precisely the number of times they are co-present in the same chunk, so

问题 I am looking for some guidance. I have a data form field which I am inserting into a table and am looking to association the data with the id's of other relevant data. I was wondering if there was recommended way to insert an array of relevant Id's in relation to the information I am referring too. Below is what Im thinking... Eg. php reads <?php $name = $_POST['name']; $info = $_POST['information']; $id = $_POST['id']; $family = array(); ?> <?php $select = "SELECT * FROM `names_family` WHERE

问题 I found this recently when trying to do bidirectional relationships in rails (http://www.dweebd.com/sql/modeling-bidirectional-graph-edges-in-rails/) class Befriending < ActiveRecord::Base belongs_to :initiator, :class_name => :User belongs_to :recipient, :class_name => :User after_create do |b| BefriendingEdge.create!(:user => b.initiator, :befriending => b) BefriendingEdge.create!(:user => b.recipient, :befriending => b) end end class BefriendingEdge < ActiveRecord::Base belongs_to :user

问题 I am studying for exams and am failing to find a solid criteria by which I can determine if the Cartesian Product x is to be used or if Natural Join |X| is to be used. I had come up with a rough guide that: "If you need to project an attribute that has the same name as an attribute in the table to be joined you must use x and state the table names to be projected: tableA.colname1 = tableB.colname1 " This however doesn't follow some of the solutions in my notes and my lecturer seems to use x