Employee Database

Background

Conduct research on employees of the corporation from the 1980s and 1990s. However, all that remains of the database of employees from that period are six CSV files. Design tables to hold data in the CSVs, import the CSVs into a SQL database, and answer questions about the data.

Methods

Data Modeling

First, inspect the CSVs and sketch out an ERD of the tables. I used http://www.quickdatabasediagrams.com to produce the data map below:

Data Engineering

• Create a table schema for each of the six CSV files and specify the data types, primary keys, foreign keys, and other constraints.
  • Primary keys should be reserved for unique columes!
  • Create tables in the correct order to handle foreign keys.

Data Analysis

With the complete database, produce the following:

1. List the following details of each employee: employee number, last name, first name, sex, and salary.

select e.emp_no, e.first_name, e.last_name, e.gender, s.Salary
from public."Employees" e
inner join public."Salaries" s on e.emp_no = s.emp_no;

2. List first name, last name, and hire date for employees who were hired in 1986.

select e.first_name, e.last_name, e.hire_date
from public."Employees" e
where e.hire_date > '1986-01-01' and e.hire_date < '1986-12-31';

3. List the manager of each department with the following information: department number, department name, the manager's employee number, last name, first name.

select ma.dept_no, dep.dept_name, e.emp_no, e.last_name, e.first_name
from public."Employees" e
inner join public."Managers" ma on e.emp_no = ma.emp_no
inner join public."Departments" dep on dep.dept_no = ma.dept_no;

4. List the department of each employee with the following information: employee number, last name, first name, and department name.

select e.emp_no, e.last_name, e.first_name, dep.dept_name
from public."Employees" e
inner join public."Dept_Emp" de on de.emp_no = e.emp_no 
inner join public."Departments" dep on de.dept_no = dep.dept_no;

5. List first name, last name, and sex for employees whose first name is "Hercules" and last names begin with "B."

select e.first_name, e.last_name, e.gender
from public."Employees" e
where e.first_name = 'Hercules' and e.last_name like 'B%';

6. List all employees in the Sales department, including their employee number, last name, first name, and department name.

select e.emp_no, e.last_name, e.first_name, d.dept_name
from public."Employees" e
inner join public."Dept_Emp" de on de.emp_no = e.emp_no
inner join public."Departments" d on d.dept_no = de.dept_no
where d.dept_name = 'Sales';

7. List all employees in the Sales and Development departments, including their employee number, last name, first name, and department name.

select e.emp_no, e.last_name, e.first_name, d.dept_name
from public."Employees" e
inner join public."Dept_Emp" de on de.emp_no = e.emp_no
inner join public."Departments" d on d.dept_no = de.dept_no
where d.dept_name = 'Sales' or d.dept_name = 'Development';

8. In descending order, list the frequency count of employee last names, i.e., how many employees share each last name.

select e.last_name, 
count (e.last_name) as "Count" from public."Employees" e
group by e.last_name
order by "Count" desc;

9. Search for ID number: 499942

Select * from public."Employees"
where emp_no = 499942;