SQL 1: Terminology

Database, Structured Query Language, Relational vs Non Relational Database, SQL Queries, etc.

“If you don’t know SQL, no sane company will hire you” - Mike West. Congrats, by reading this post, you now know more about SQL than most people enrolled in BootCamps. You’re on your path to actually having a real shot at getting hired.

Unless you work in the data engineering side of things, you will focus on how to manipulate data using SQL. That’s what the beginner section will focus on.

If you are completely new to SQL, you can use a simple tool such as Online SQL Compiler. It’s nice because it’ll color in some of the clauses for you, and fill in some code for you.

You can use the Import button to upload a simple csv, and voila your table is ready.

If you are comfortable in your SQL skills, you can use the SQLDF library in R. In here, the variables you create are tables, and you can execute simple sql code, and just get some nice practice in.

You can use sqldf for some quick sql practice once ready.

Table of Contents

1. Database

2. Structured Query Language

3. Relational vs Non-Relational Databases

4. SQL Queries

   1. Transactions

   2. Statements

5. DDL, DML, TLC

   1. Data Definition Language

   2. Data Manipulation Language

   3. Transaction Language Control

6. Exercises

Let’s begin.

1 - Database

In simple English, a database can be anything that gathers, and consolidates data.

In the real world, when someone is referring to a Database, they usually mean a Relational DataBase Management System (RDBMS). RDMS is a database, that stores 1 or more tables. Here is a simple image of how SQL communicates with a RDBMS.

SQL goes into RDBMS, the table comes out.

2 - Structured Query Language

To communicate with the database, we need to use a simple language that it understands. Structured Query Language (SQL) is a popular language that is used to communicate with several RDBMS.

SQL lets a user create some code. Then use this to query the database, and it lets you pull the entries that you were after.
You can think of this as a simple file cabinet:

• Database = File Cabinet

• Drawer = Table

• Folders = Rows (Entries)

SQL Visualized

Of course, we also have queries you can send to the file cabinet to create more folders (rows), and drawers (tables).