https://github.com/apollo-level2-web-dev/b3-psql-conceptual-session

https://github.com/apollo-level2-web-dev/b3-psql-conceptual-session

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• Host: GitHub
• URL: https://github.com/apollo-level2-web-dev/b3-psql-conceptual-session
• Owner: Apollo-Level2-Web-Dev
• Created: 2024-10-21T17:07:18.000Z (3 months ago)
• Default Branch: main
• Last Pushed: 2024-10-21T17:08:03.000Z (3 months ago)
• Last Synced: 2024-10-22T06:44:05.785Z (3 months ago)
• Size: 2.93 KB
• Stars: 2
• Watchers: 0
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# **SQL Concepts and Tasks: Employees and Departments Database (PostgreSQL)**

## **Introduction**

In this session, we will explore fundamental SQL concepts using **PostgreSQL** by creating and manipulating two related tables: **employees** and **departments**. The **employees** table will store information about employees, including their names, hire dates, salaries, and active status. The **departments** table will hold details about various departments within an organization. Through a series of tasks, we will practice SQL operations such as creating tables, inserting data, defining constraints, querying information, and modifying tables. This hands-on approach will enhance your understanding of SQL and its practical applications in database management using PostgreSQL.

---

### **Sample Data Table 1: `employees`**

| employee_id | first_name | last_name | hire_date  | salary   | department_id | is_active |

| ----------- | ---------- | --------- | ---------- | -------- | ------------- | --------- |

| 1           | John       | Doe       | 2021-05-10 | 50000.00 | 1             | TRUE      |

| 2           | Jane       | Smith     | 2022-03-15 | 62000.00 | 2             | TRUE      |

| 3           | Alice      | Johnson   | 2023-01-20 | 55000.00 | 1             | FALSE     |

| 4           | Bob        | Davis     | 2020-11-30 | 72000.00 | 3             | TRUE      |

---

### **Sample Data Table 2: `departments`**

| department_id | department_name | manager_id |

| ------------- | --------------- | ---------- |

| 1             | Human Resources | 1          |

| 2             | Finance         | 2          |

| 3             | Engineering     | 4          |

---

### **Task List Based on the Above Tables**

#### **Task 1: Creating Tables with Multiple Columns and Data Types**

- **Create the `employees` table** with various data types like `VARCHAR`, `DATE`, `BOOLEAN`, and `NUMERIC`.

- **Create the `departments` table** with a `SERIAL` type for the primary key and a `VARCHAR` type for the department name.

- Ensure that the `first_name`, `last_name`, and `department_name` columns are `NOT NULL`.

- Add a `PRIMARY KEY` constraint to `employee_id` and `department_id`.

- Add a `FOREIGN KEY` constraint on `department_id` in the `employees` table that references `department_id` in the `departments` table.

#### **Task 2: Inserting Data and Checking Constraints**

- Insert sample records (as shown above) into the `employees` and `departments` tables.

- Attempt to insert a record where `first_name` is `NULL` to validate the `NOT NULL` constraint.

- Try to insert a record with a non-existent `department_id` to test the `FOREIGN KEY` constraint.

#### **Task 3: Querying the Data**

1. **Basic Queries:**

   - Select all active employees.

   - Find all employees in the Finance department.

2. **Aggregate Functions:**

   - Calculate the total salary for employees in the Engineering department.

   - Determine the average salary for all employees.

3. **Sorting and Aliasing:**

   - Select employee names and salaries, aliasing `first_name` as `First Name` and `salary` as `Employee Salary`.

   - Sort employees by their hire date in descending order.

4. **NULL Filtering:**

   - List all departments where the `manager_id` is NULL (if any records exist).

5. **Using `LIKE` and `BETWEEN`:**

   - Find all employees whose `last_name` starts with "J".

   - Get employees hired between `2021-01-01` and `2022-12-31`.

#### **Task 4: Modifying Tables**

- Use `ALTER TABLE` to add a new column, `phone_number`, to the `employees` table.

- Modify the `salary` column to increase its precision if necessary.

- Drop the `is_active` column from the `employees` table.

#### **Task 5: JOIN Operations**

- Write a query to join the `employees` and `departments` tables to display the department name for each employee.

- Find all employees and their manager's name (self-join if managers are also employees).

#### **Task 6: Subqueries**

- Find the highest-paid employee using a subquery.

- Retrieve all employees whose salary is above the average salary.

#### **Task 7: Views**

- Create a view called `active_employees` that shows only active employees and their departments.

- Select all data from the created view.

#### **Task 8: Indexing**

- Create an index on the `last_name` column of the `employees` table to speed up search queries.

- Drop the index if needed.

#### **Task 9: Pagination**

- Write a query to fetch the first 2 employees ordered by `employee_id`, and then implement pagination using `LIMIT` and `OFFSET`.

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# B3-psql-conceptual-session