For an instructor lead, in-depth look at learning SQL click below.
Welcome to this exciting guide where we will walk together on the path of understanding and mastering SQL (Structured Query Language). For beginners, SQL might seem intimidating, but don’t worry. I assure you that by the end of this guide, you will realize just how approachable and versatile SQL can be.
What is SQL?
SQL is a standard language for manipulating and retrieving data from relational databases. The beauty of SQL is that it is both expressive and comprehensive, allowing us to specify complex operations succinctly.
SQL Basics
Every journey starts with a first step. Let’s dive into the pool of SQL by learning the most common command: SELECT. The select statement is used to query the database and retrieve selected data that match the criteria that you specify. Here is the syntax of a basic SQL SELECT statement.
|
1 2 3 4 |
SELECT column1, column2, ..., columnN FROM table_name; |
The above syntax selects from the “table_name” with the specific columns you want. If you want to select everything from the table, you can use an asterisk (*) in place of columns.
|
1 2 3 4 |
SELECT * FROM table_name; |
SQL Conditions and Filters
Often times, selecting everything from the table is overwhelming, and we don’t usually need all of the data. This is where Filtering comes into play. Using the WHERE clause in SQL, we can filter out the data we don’t need.
|
1 2 3 4 5 |
SELECT column1, column2, ..., columnN FROM table_name WHERE condition; |
For instance, let’s say we have a table named “Employees” and we want to select only those employees who have a salary greater than 5000.
|
1 2 3 4 5 |
SELECT * FROM Employees WHERE Salary > 5000; |
SQL Joins
In relational databases, data is often split into different tables to avoid redundancy. But such a design requires that we join tables together to get certain information. SQL provides several types of joins to get data from multiple tables. Here is a simple example of an INNER JOIN:
|
1 2 3 4 5 6 |
SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate FROM Orders INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID; |
The above SQL statement selects OrderID, CustomerName, and OrderDate from the “Orders” and “Customers” tables, where the CustomerID matches in both tables.
Wrap Up
SQL is a powerful language with much more functionality than can be covered in a beginner’s guide. This introduction only scratched the surface of topics like Aggregation, Grouping and much more. However, understanding these basics will go a long way in mastering SQL. The key is to keep practising! Keep experimenting with different queries, and you’ll find that SQL is not only useful, but also really fun!