For an instructor lead, in-depth look at learning SQL click below.
L Fundamentals: Understanding Relational Database Systems
## Introduction
SQL, or Structured Query Language, is the language of choice for interacting with and extracting data from relational databases. Commonly used in various forms of data analysis, SQL allows users to view specific pieces of data within a database, make changes, create new tables and perform a whole host of other tasks. This blog post will delve into the fundamentals of SQL in relation to relational databases, demonstrating key concepts with relevant SQL code examples!
## What are Relational Databases?
Relational databases organize data into one or more tables (or “relations”) of rows and columns, with a unique key for each row. Generally, each table/relation corresponds to one “entity type” (such as customer or product). The rows represent instances of that type of entity and the columns are attributes of that entity (such as customer name or product price).
## Understanding SQL Syntax
SQL is a standardized language that uses English-like commands, enabling users to easily understand and write code. The foundation of SQL revolves around the basic commands like SELECT, FROM, WHERE, GROUP BY, HAVING and ORDER BY.
## Writing Your First SQL Query
Selecting Everything from a Table
The most basic SQL command is the ‘SELECT’ statement. This will return every row from a table of your choice. Following command returns all rows and columns from the table ‘Customers’:
|
1 2 3 |
SELECT * FROM Customers; |
Selecting Specific Columns
If you want to select certain columns from a table, you’ll use the same ‘SELECT’ statement, but replace the asterisk (*) with the names of the columns you want to extract. The following command will return only the ‘FirstName’ and ‘LastName’ columns from the ‘Customers’ table:
|
1 2 3 |
SELECT FirstName, LastName FROM Customers; |
## Filtering Your Data
Using the WHERE Clause
The ‘WHERE’ clause in SQL is used to filter records based on specific conditions. The following query will return all data from the ‘Customers’ table where the ‘Country’ is ‘Germany’:
|
1 2 3 |
SELECT * FROM Customers WHERE Country='Germany'; |
## Conclusion
SQL is a highly efficient language designed for managing data stored in a Relational Database Management System (RDBMS), or for stream processing in a Relational Data Stream Management System (RDSMS). It is hugely popular due to its flexibility and powerful commands, with the ability to tackle massive databases with millions of rows with relative simplicity.
The next step in your journey to mastering SQL is understanding how to join tables, manipulate data, and use functions. But that’s for another post! Happy querying!