I am designing a database for school.
Requirements
Professors have an SSN, a name, an age, gender, a rank, and a research specialty
Professors work in exactly one department
Departments have a department number, a department name, and a main office
Departments must have one professor (known as the chairman) who runs the department
My current schema for "Professors" and "Departments"
CREATE DOMAIN SSN AS CHAR(11) CONSTRAINT validSSN CHECK (VALUE ~* "^\d{3}-\d{2}-\d{4}$");
CREATE TABLE Persons (
person_id INT PRIMARY KEY AUTO_INCREMENT,
ssn SSN NOT NULL CONSTRAINT mustBeDifferent UNIQUE,
name VARCHAR(255) NOT NULL,
age INT NOT NULL CONSTRAINT nonnegativeAge CHECK(age >= 0),
gender CHAR(1) CONSTRAINT mustBeMaleOrFemale CHECK(gender = "M" OR gender = "F") NOT NULL,
);
CREATE TABLE Professors (
ranking INT NOT NULL CONSTRAINT positiveRanking CHECK(ranking > 0),
research_specialty VARCHAR(255) NOT NULL,
department_id INT NOT NULL REFERENCES Departments(department_number)
) INHERITS(Persons);
CREATE TABLE Departments (
department_number INT PRIMARY KEY AUTO_INCREMENT,
department_name VARCHAR(255) NOT NULL,
main_office VARCHAR(255) NOT NULL,
chairman_id INT REFERENCES Professors(person_id)
);
I have a foreign key in the "Professors" table that references the "Departments" table and a foreign key in the "Departments" table that references the "Professors" table.
Is there any way that I could go about resolving this issue?
I see a few problems:
professors should not inherit from persons, but reference it with a foreign key.
Otherwise you cannot guarantee uniqueness of the primary key.
Don't store the age in persons, but the birthday.
Otherwise your data will grow invalid pretty quickly.
If there is no length limit dictated by the application, don't use varchar(255), but use text.
Related
New to SQL, can't figure out what is wrong in my given code. all it says is:
Incorrect syntax near 'DESCRIBE'. [41,1]
I have tried taking off the semi-colons. I really just don't know what it wants from me.
Here is my code. Anything helps, thank you!
-- Write the query to create the 4 tables below.
CREATE TABLE client (
id INT NOT NULL IDENTITY(1,1),
first_name VARCHAR(255) NOT NULL,
last_name VARCHAR(255) NOT NULL,
dob DATE NOT NULL,
PRIMARY KEY (id),
CONSTRAINT (full_name) UNIQUE (first_name, last_name)
);
CREATE TABLE employee (
id INT NOT NULL IDENTITY(1,1),
first_name VARCHAR(255) NOT NULL,
last_name VARCHAR(255) NOT NULL,
dob DATE NOT NULL,
date_joined DATE NOT NULL,
CONSTRAINT (full_name) UNIQUE (first_name, last_name),
PRIMARY KEY (id)
);
CREATE TABLE project (
id INT NOT NULL IDENTITY(1,1),
cid INT NOT NULL,
name VARCHAR(255) NOT NULL,
notes TEXT,
UNIQUE (name),
FOREIGN KEY (cid) REFERENCES client(id)
);
CREATE TABLE works_on (
eid INT NOT NULL,
pid INT NOT NULL,
start_date DATE NOT NULL,
PRIMARY KEY (eid, pid),
FOREIGN KEY (eid) REFERENCES employee(id),
FOREIGN KEY (pid) REFERENCES project(id)
);
-- Leave the queries below untouched. These are to test your submission correctly.
-- Test that the tables were created
DESCRIBE client;
DESCRIBE employee;
DESCRIBE project;
DESCRIBE works_on;
-- Test that the correct foreign keys were created
SELECT TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME,REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE REFERENCED_TABLE_SCHEMA = 'grade';
For MariaDB (and MySQL) the correct syntax for IDENTITY(1,1), is AUTO_INCREMENT, and CONSTRAINT names are not enclosed in (). Any column that is defined as AUTO_INCREMENT must also be declared as a PRIMARY KEY (this is only an issue with the project table). So your CREATE TABLE commands should look like this:
CREATE TABLE client (
id INT NOT NULL AUTO_INCREMENT,
first_name VARCHAR(255) NOT NULL,
last_name VARCHAR(255) NOT NULL,
dob DATE NOT NULL,
PRIMARY KEY (id),
CONSTRAINT full_name UNIQUE (first_name, last_name)
);
CREATE TABLE employee (
id INT NOT NULL AUTO_INCREMENT,
first_name VARCHAR(255) NOT NULL,
last_name VARCHAR(255) NOT NULL,
dob DATE NOT NULL,
date_joined DATE NOT NULL,
CONSTRAINT full_name UNIQUE (first_name, last_name),
PRIMARY KEY (id)
);
CREATE TABLE project (
id INT NOT NULL AUTO_INCREMENT,
cid INT NOT NULL,
name VARCHAR(255) NOT NULL,
notes TEXT,
PRIMARY KEY (id),
UNIQUE (name),
FOREIGN KEY (cid) REFERENCES client(id)
);
CREATE TABLE works_on (
eid INT NOT NULL,
pid INT NOT NULL,
start_date DATE NOT NULL,
PRIMARY KEY (eid, pid),
FOREIGN KEY (eid) REFERENCES employee(id),
FOREIGN KEY (pid) REFERENCES project(id)
);
Demo on dbfiddle
CREATE TABLE EMPLOYEE (
EID CHAR(3) NOT NULL PRIMARY KEY,
ENAME VARCHAR2(50) NOT NULL,
JOB_TYPE VARCHAR2(50) NOT NULL,
MANAGER CHAR(3) FOREIGN KEY REFERENCES EMPLOYEE(EID),
HIRE_DATE DATE NOT NULL,
DNO INTEGER FOREIGN KEY REFERENCES DEPARTMENT(DNO),
COMMISSION DECIMAL(10,2),
SALARY DECIMAL(7,2) NOT NULL,
);
CREATE TABLE DEPARTMENT (
DNO INT NOT NULL PRIMARY KEY,
DNAME VARCHAR(50),
LOCATION VARCHAR(50) DEFAULT('NEW DELHI')
);
in creation of the employee table
this is giving me an error of right parenthesis
and the department table is already created
You have an extra comma in the line
SALARY DECIMAL(7,2) NOT NULL,
Delete that comma and the Employee table should be created.
You need to Create the Department Table first to use one of its
Columns as FOREIGN KEY.
Also, check your database. There might already be a Department Table. To avoid getting that error when the table needed is already created, use the keyword IF NOT EXISTS
CREATE TABLE IF NOT EXISTS Department(
DNO INT NOT NULL PRIMARY KEY,
DNAME VARCHAR(50),
LOCATION VARCHAR(50) DEFAULT('NEW DELHI')
);
The error is caused by the trailing comma, but you have other issues:
The FOREIGN KEY is not needed for an inline reference.
You need to define the tables in the right order.
So . . .
CREATE TABLE DEPARTMENT (
DNO INT NOT NULL PRIMARY KEY,
DNAME VARCHAR(50),
LOCATION VARCHAR(50) DEFAULT('NEW DELHI')
);
CREATE TABLE EMPLOYEE (
EID CHAR(3) NOT NULL PRIMARY KEY,
ENAME VARCHAR2(50) NOT NULL,
JOB_TYPE VARCHAR2(50) NOT NULL,
MANAGER CHAR(3) REFERENCES EMPLOYEE(EID),
HIRE_DATE DATE NOT NULL,
DNO INTEGER REFERENCES DEPARTMENT(DNO),
COMMISSION DECIMAL(10,2),
SALARY DECIMAL(7,2) NOT NULL
);
Here is an example of it working.
For now I have only two tables
CREATE TABLE IF NOT EXISTS company (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name VARCHAR (250) NOT NULL
);
CREATE TABLE IF NOT EXISTS employee (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name VARCHAR (250),
company_id INT,
FOREIGN KEY (company_id) REFERENCES Company (id)
);
I need to create one or two tables to store employees and companies statistic. For employee statistic I need to remember all previous companies of this employee and of cause hire dates and resign dates. For company statistic I need to remember all resigned employees. What is the best way to organize DB structure in my case?
Since you have many-to-many relationship, you need an aggregate table company_employee that will have combined primary key, so you need:
CREATE TABLE IF NOT EXISTS company (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name VARCHAR (250) NOT NULL
);
CREATE TABLE IF NOT EXISTS employee (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name VARCHAR (250)
);
CREATE TABLE IF NOT EXISTS company_employee (
company_id INT NOT NULL,
employee_id INT NOT NULL,
hire_date DATE,
resign_date DATE,
FOREIGN KEY (company_id) REFERENCES Company (id),
FOREIGN KEY (employee_id) REFERENCES Employee (id)
);
So, if you want anything from aggregate table, just use JOIN on key of appropriate table.
the Staff table references the branch table
CREATE TABLE Staff(
StaffNo VARCHAR(5) NOT NULL,
firstName VARCHAR(15) NOT NULL UNIQUE,
lastName VARCHAR(15) NOT NULL,
position VARCHAR(10) NOT NULL,
salary INTEGER
DEFAULT 3000,
CHECK (salary BETWEEN 3000 AND 25000),
email VARCHAR(25),
branchNo CHAR(6) NOT NULL,
PRIMARY KEY (StaffNo),
FOREIGN KEY (branchNo) REFERENCES Branch (branchNo));
and at the same time the branch table references the Staff table
create table Branch(
branchNo char(6) not null primary key,
street varchar(30) not null,
city varchar(20),
postCode char(5) not null,
ManagerNo varchar(5) not null,
foreign key (ManagerNo) references Staff(StaffNo));
Since your tables reference each other in the Foreign Keys you will get an error on either table creation if the other table has not been created yet. I would suggest that you remove the creation of the FOREIGN KEYs to separate ALTER TABLE statements:
CREATE TABLE Staff(
StaffNo VARCHAR(5) NOT NULL,
firstName VARCHAR(15) NOT NULL UNIQUE,
lastName VARCHAR(15) NOT NULL,
position VARCHAR(10) NOT NULL,
salary INTEGER
DEFAULT 3000,
CHECK (salary BETWEEN 3000 AND 25000),
email VARCHAR(25),
branchNo CHAR(6) NOT NULL,
PRIMARY KEY (StaffNo)
);
create table Branch(
branchNo char(6) not null primary key,
street varchar(30) not null,
city varchar(20),
postCode char(5) not null,
ManagerNo varchar(5) not null
);
alter table staff
add constraint fk1_branchNo foreign key (branchNo) references Branch (branchNo);
alter table branch
add constraint fk1_ManagerNo foreign key (ManagerNo) references Staff (StaffNo);
See SQL Fiddle with Demo
You can remove one reference from one table and keep the other.then you can retrieve data using the remainig reference.Is there any problem with that?
I'm trying to create a table that has a primary key (Department_ID) that auto assigns(not hard). However the assignment would be based on the exsisting value in another column(Department_Name). So for example if its the department_name payroll the department_ID would be 1 for example. If I tried to insert into and had to add another payroll employee it would not auto increment. It would assign value 1 to it. I assume its constraint I am looking for, but have no idea if I'm looking at this wrong or how to write it. Here's what I have so far:
CREATE TABLE tblDepartment
(
Department_ID int NOT NULL IDENTITY,
Department_Name varchar(255) NOT NULL,
Division_Name varchar(255) NOT NULL,
City varchar(255) default 'sometown' NOT NULL,
Building int default 1 NOT NULL,
Phone varchar(255) NOT NULL,
PRIMARY KEY (Department_ID)NOT NULL,
Check (Building >=1 AND Building <= 10 )
)
CREATE TABLE tblEmployee
(
Employee_ID int NOT NULL IDENTITY,
Department_ID int ,
Employee_Name varchar(255),
Social_Security_Number varchar(255),
Work_Phone varchar(255),
Position varchar(255),
Hire_Date datetime,
Birth_Date datetime,
FOREIGN KEY (Department_ID) REFERENCES tblDepartment(Department_ID)
)
Thanks for the help!
You shouldn't need a Department record per employee. You'll only have one Department record per department. You'll insert the Department.Department_ID value from the corresponding Department record into the Employee.Department_ID field when you insert an Employee record.
An autoincrement field for Department.Department_ID should be fine.
According to your schema, you already have a constraint that enforces this.
A TRIGGER on insert into tblEmployee that reads tblDepartment and sets the key accordingly might be a solution.
What happens if an employee changes department?