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Conduct a research project on employees of the corporation from the 1980s and 1990s. All that remain of the database of employees from that period are six CSV files.

Design the tables to hold data in the CSVs, import the CSVs into a SQL database, and answer questions about the data. In other words, perform the following:

  1. Data Modeling

  2. Data Engineering

  3. Data Analysis


Data Modeling

Inspect the CSVs and sketch out an ERD of the tables using QuickDBD




Creating tables:


-- Data Engineering --
-- Drop Tables if Existing
DROP TABLE IF EXISTS departments;
DROP TABLE IF EXISTS dept_emp;
DROP TABLE IF EXISTS dept_manager;
DROP TABLE IF EXISTS employees;
DROP TABLE IF EXISTS salaries;
DROP TABLE IF EXISTS titles;

-- Exported from QuickDBD: Specifying Data Types, Primary Keys & Foreign Keys 
-- Import CSV Files Into Corresponding SQL Table
CREATE TABLE "departments" (
    "dept_no" VARCHAR   NOT NULL,
    "dept_name" VARCHAR   NOT NULL,
    CONSTRAINT "pk_departments" PRIMARY KEY (
        "dept_no"
     )
);

CREATE TABLE "dept_emp" (
    "emp_no" INT   NOT NULL,
    "dept_no" VARCHAR   NOT NULL,
    "from_date" DATE   NOT NULL,
    "to_date" DATE   NOT NULL
);

CREATE TABLE "dept_manager" (
    "dept_no" VARCHAR   NOT NULL,
    "emp_no" INT   NOT NULL,
    "from_date" DATE   NOT NULL,
    "to_date" DATE   NOT NULL
);

CREATE TABLE "employees" (
    "emp_no" INT   NOT NULL,
    "birth_date" DATE   NOT NULL,
    "first_name" VARCHAR   NOT NULL,
    "last_name" VARCHAR   NOT NULL,
    "gender" VARCHAR   NOT NULL,
    "hire_date" DATE   NOT NULL,
    CONSTRAINT "pk_employees" PRIMARY KEY (
        "emp_no"
     )
);

CREATE TABLE "salaries" (
    "emp_no" INT   NOT NULL,
    "salary" INT   NOT NULL,
    "from_date" DATE   NOT NULL,
    "to_date" DATE   NOT NULL
);

CREATE TABLE "titles" (
    "emp_no" INT   NOT NULL,
    "title" VARCHAR   NOT NULL,
    "from_date" DATE   NOT NULL,
    "to_date" DATE   NOT NULL
);

ALTER TABLE "dept_emp" ADD CONSTRAINT "fk_dept_emp_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");

ALTER TABLE "dept_emp" ADD CONSTRAINT "fk_dept_emp_dept_no" FOREIGN KEY("dept_no")
REFERENCES "departments" ("dept_no");

ALTER TABLE "dept_manager" ADD CONSTRAINT "fk_dept_manager_dept_no" FOREIGN KEY("dept_no")
REFERENCES "departments" ("dept_no");

ALTER TABLE "dept_manager" ADD CONSTRAINT "fk_dept_manager_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");

ALTER TABLE "salaries" ADD CONSTRAINT "fk_salaries_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");

ALTER TABLE "titles" ADD CONSTRAINT "fk_titles_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");



Display Table Data


-- Query * FROM Each Table Confirming Data
SELECT * FROM departments;
SELECT * FROM dept_emp;
SELECT * FROM dept_manager;
SELECT * FROM employees;
SELECT * FROM salaries;
SELECT * FROM titles;


Data Analysis

Once there is a complete database, do the following:


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

SELECT employees.emp_no, employees.last_name, employees.first_name, employees.gender, salaries.salary
FROM employees
JOIN salaries
ON employees.emp_no = salaries.emp_no;


List employees who were hired in 1986.

SELECT first_name, last_name, hire_date 
FROM employees
WHERE hire_date BETWEEN '1986-01-01' AND '1987-01-01';


List the manager of each department with the following information: department number, department name, the manager's employee number, last name, first name, and start and end employment dates.

SELECT departments.dept_no, departments.dept_name, dept_manager.emp_no, employees.last_name, employees.first_name, dept_manager.from_date, dept_manager.to_date
FROM departments
JOIN dept_manager
ON departments.dept_no = dept_manager.dept_no
JOIN employees
ON dept_manager.emp_no = employees.emp_no;


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

SELECT dept_emp.emp_no, employees.last_name, employees.first_name, departments.dept_name
FROM dept_emp
JOIN employees
ON dept_emp.emp_no = employees.emp_no
JOIN departments
ON dept_emp.dept_no = departments.dept_no;


List all employees whose first name is "Hercules" and last names begin with "B."

SELECT first_name, last_name
FROM employees
WHERE first_name = 'Hercules'
AND last_name LIKE 'B%';


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

SELECT dept_emp.emp_no, employees.last_name, employees.first_name, departments.dept_name
FROM dept_emp
JOIN employees
ON dept_emp.emp_no = employees.emp_no
JOIN departments
ON dept_emp.dept_no = departments.dept_no
WHERE departments.dept_name = 'Sales';


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

SELECT dept_emp.emp_no, employees.last_name, employees.first_name, departments.dept_name
FROM dept_emp
JOIN employees
ON dept_emp.emp_no = employees.emp_no
JOIN departments
ON dept_emp.dept_no = departments.dept_no
WHERE departments.dept_name = 'Sales' 
OR departments.dept_name = 'Development';


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

SELECT last_name,
COUNT(last_name) AS "frequency"
FROM employees
GROUP BY last_name
ORDER BY 

COUNT(last_name) DESC;



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