Little by little I am moving on and understanding sql. Below I have 4 tables. I am trying to work through the “many to many” and “one to many”. Earlier on a similar question I was trying to figure out academies to courses and vice versa. Now it was explained to me that one table was for the course and the other table(academy_course) was for the relationship table where I can store the many-to-many relationships. Do I need to apply the same logic for instructors affiliated with an academy? A unique instructor per academy.
CREATE TABLE academy
(
academy_id int(11) not null auto_increment,
name varchar(25) not null,
primary key (id),
);
CREATE TABLE course
(
course_id int(11) not null auto_increment,
course_name VARCHAR(50) NOT NULL ,
primary key (course_id),
);
CREATE TABLE academy_course
(
academy_id int(11) not null,
course_id int(11) not null ,
primary key (academy_id, course_id),
foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade,
foreign key (course_id) REFERENCES course (course_id) on delete cascade
);
CREATE TABLE instructors
(
instructor_id VARCHAR(10) NOT NULL ,
academy_id INT NOT NULL ,
instructor_name VARCHAR(50) NOT NULL ,
primary key (instructor_id),
foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade
);
In the instructor only teaches at one academy, then it's easy to just have an academy_id like you have there.
If the instructor can teach at different academies, then yes. You should create a table for that:
CREATE TABLE academy_instructor
(
academy_id int(11) not null,
instructor_id int(11) not null ,
primary key (academy_id, instructor_id),
foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade,
foreign key (instructor_id) REFERENCES instructor (instructor_id) on delete cascade
);
If one each academy has only one instructor then I would consider adding
instructor_id to the academy_course table.
If the same instructor can teach at different academies (which does happen), then it would be a many-to-many. If no instructor does that, it would be a one-to-many.
Related
In my situation i have
TABLE vehicles (
id int(11) NOT NULL AUTO_INCREMENT,
transaction_type varchar(45),
PRIMARY KEY (`id`)
/* all other values of vehicle */
)
TABLE Origination(
id int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
)
TABLE Additions(
id int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
)
So i have this new vehicles table that originate either from Origination, or Additions. The reason it can come from two tables is business needs, it either orginates for the origin or it originates from a special addition after the fact. I'm unsure how to connect a "vehicle" relation to both tables as the id can come from either.
So i added a transaction_type field, where if type is "Additions" join tables based on Additions Id. Else if type is "origination" join on Origination Id.
So i have a Two Key "1 to many" relationship. is this a valid and useable design practice? I am not a database person, but am trying to learn how to handle this is the best way.
From what I understand you want a main table containing ALL your vehicles and two separate tables that add different data to those vehicles. This is how I'd make that work. If you be more specific about what each table does I can be of more help.
TABLE Vehicle (
id int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
/* all other values of vehicle */
)
TABLE Origination (
id int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
)
TABLE Addition (
id int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
)
TABLE Vehicle_Origination (
origination_id int(11),
vehicle_id int(11),
FOREIGN KEY (origination_id) REFERENCES Origination (id),
FOREIGN KEY (vehicle_id) REFERENCES Vehicle (id)
)
TABLE Vehicle_Addition (
addition_id int(11),
vehicle_id int(11),
FOREIGN KEY (addition_id) REFERENCES Addition (id),
FOREIGN KEY (vehicle_id) REFERENCES Vehicle (id)
)
Having some trouble adding a relation between tables
CREATE TABLE IF NOT EXISTS `employees` (
`emp_id` int(11) NOT NULL auto_increment,
`emp_fname` char(50) NOT NULL,
`emp_sname` char(50) NOT NULL,
`emp_patr` char(50) NOT NULL,
`emp_birth` datetime NOT NULL default CURRENT_TIMESTAMP,
`isInCharge` boolean default NULL,
`depart_id` int(11) NOT NULL,
PRIMARY KEY (`emp_id`)
) ENGINE=InnoDB DEFAULT CHARSET=cp1251;
CREATE TABLE IF NOT EXISTS `department` (
`depart_id` int(11) NOT NULL auto_increment,
`depart_name` char(50) NOT NULL,
PRIMARY KEY (`depart_id`),
FOREIGN KEY (depart_id) REFERENCES employees (depart_id) on delete
cascade on update cascade
) ENGINE=InnoDB DEFAULT CHARSET=cp1251;
Cannot add foreign key constraint
What is going wrong? I need to make possible for many employees to be in one department.
Also, how can I generate a random birth date from 1950 to 1990?
Your foreign key is in the wrong place. It belongs in the employees table not the department table. And it should be:
FOREIGN KEY (depart_id) REFERENCES department(depart_id) on delete cascade on update cascade
This should be easy to remember. You define the primary key in the table where the column is unique. You define the foreign key in all tables that refer to that primary key.
It should be the other way around right? dept_Id in Employee shall be foriegn key referencing the primary key Dept_ID of Department.
It's currently i am using .In that i want to reduces the association table .And attain the same objective.Kindly some one help me to find solution.
CREATE TABLE sys_student_t (
student_id MEDIUMINT NOT NULL AUTO_INCREMENT,
student_name VARCHAR(255),
PRIMARY KEY (student_id)
);
CREATE TABLE sys_classrooms_t (
classroom_id MEDIUMINT NOT NULL AUTO_INCREMENT,
classroom_name VARCHAR(255),
PRIMARY KEY (classroom_id)
);
CREATE TABLE student_classroom_association_t (
association_id MEDIUMINT NOT NULL AUTO_INCREMENT,
classroom_id MEDIUMINT NOT NULL,
student_id MEDIUMINT NOT NULL,
FOREIGN KEY (student_id) REFERENCES sys_student_t (student_id),
FOREIGN KEY (classroom_id) REFERENCES sys_classrooms_t (classroom_id),
PRIMARY KEY (association_id)
);
Here is fiddle link :- http://www.sqlfiddle.com/#!9/ada4fd/2
thanks
A "Many-To-Many" relationship will always require an additional table. The only thing you can do is changing the primary key of the association table to the pair student_id and classroom_id.
CREATE TABLE student_classroom_association_t (
classroom_id MEDIUMINT NOT NULL,
student_id MEDIUMINT NOT NULL,
FOREIGN KEY (student_id) REFERENCES sys_student_t (student_id),
FOREIGN KEY (classroom_id) REFERENCES sys_classrooms_t (classroom_id),
PRIMARY KEY (student_id, classroom_id)
);
I am working with mysql and running into a little confusion. I have created two tables academy and courses. I am needing help in determining how to structure the table fields. For example the one to many schema. One academy can offer many courses and a course can be offered with many academies. Is the structure for the tables below correct?
create table academy
(
academy_id int(11) not null auto_increment,
course_id int() NOT NULL ,
name varchar(25) not null,
primary key (id),
);
CREATE TABLE course
(
course_id int(11) not null auto_increment,
course_name VARCHAR(50) NOT NULL ,
primary key (course_id),
foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade
);
Example of desired result
id Name Course
1 The Alamo School 125 Intro to Programming
2 Bearcat High School 125 Intro to Programming
What you really need is a table for the academies, one for the courses and a relationship table where you can store the many-to-many relationships. I leave to you the query to get the result you are looking for :)
CREATE TABLE academy
(
academy_id int(11) not null auto_increment,
name varchar(25) not null,
primary key (id),
);
CREATE TABLE course
(
course_id int(11) not null auto_increment,
course_name VARCHAR(50) NOT NULL ,
primary key (course_id),
);
CREATE TABLE accademy_course
(
academy_id int(11) not null,
course_id int(11) not null ,
primary key (academy_id, course_id),
foreign key (academy_id) REFERENCES academy (academy_id) on delete cascade,
foreign key (course_id) REFERENCES course (course_id) on delete cascade
);
In cakephp, I have Company and Profile model. I would like to establish Company has 0 or 1 Profile relationship. Is it appropriate to use Company hasOne Profile, and Profile belongsTo Company? Is there any implication I need to be aware of? The table's schema is below. Thanks.
create table companies (
id char(36) NOT NULL,
type int(10) NOT NULL,
primary key (id)
);
create table profiles (
id char(36) NOT NULL,
company_id char(36) NOT NULL,
provider_contact varchar(255) NULL,
primary key (id),
unique key (company_id),
foreign key (company_id) references companies(id)
);
Yes you can use the hasOne/belongsTo Relationship, if a Company has no Profile the sub-array will be empty.
In your profiles table you should use company_id to follow the Cake naming conventions.
To follow CakePHP's conventions, the field needs to be company_id, not companies_id.
The foreign key constraint is up to you. I typically don't add them. The unique constraint seems incorrect. This would imply that there can only be one profile per company. Which is not the same as a company can have 0 or 1 profiles.
Stick to conventions.
You need to adjust your schema to do that
create table companies (
id int(11) NOT NULL,
type int(11) NOT NULL,
primary key (id)
);
create table profiles (
id int(11) NOT NULL,
company_id int(11) NOT NULL,
provider_contact varchar(255) NULL,
primary key (id),
unique key (company_id),
foreign key (company_id) references companies(id)
);
It is company_id as others have mention. And also, ids have to be ints, and autoincremental. It's a pain to have them as chars.