For an instructor lead, in-depth look at learning SQL click below.
Welcome to our first lesson on SQL, the most popular language for managing and manipulating databases. Whether you’re from a technical or non-technical background, understanding SQL is a great asset to have under your belt. Let’s start our journey!
What is SQL?
SQL, or Structured Query Language, is a programming language used to communicate with and manipulate databases. It is particularly useful in handling structured data, i.e., data incorporating relations among entities and variables.
Writing Your First SQL Query
The true power of SQL lies in its ability to perform complex queries – asking questions about your data, so let’s start with a simple one.
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/* An example of a basic SQL query. */ SELECT * FROM Employees; |
This command retrieves all data from the ‘Employees’ table.
Filtering Your Results – The WHERE clause
Often, you’ll want to filter your results based on certain conditions. This is where the WHERE clause comes into play. Let’s suppose we want to select only the employees with a salary over 50000.
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/* An example of using WHERE to filter results. */ SELECT * FROM Employees WHERE salary > 50000; |
Sorting Your Results – The ORDER BY Clause
To sort your results in a particular order, SQL provides the ORDER BY clause. For example, we could order the employees by their first names.
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/* An example of using ORDER BY to sort results. */ SELECT * FROM Employees ORDER BY first_name; |
Summarizing Your Data – The GROUP BY clause and Aggregate Functions
SQL allows us to group data in various ways to help extract useful insights.
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/* An example of using GROUP BY with an aggregate function (SUM). */ SELECT department, SUM(salary) FROM Employees GROUP BY department; |
This query will provide the total salary expense for each department in the ‘Employees’ table.
Conclusion
And there we have it – your first steps into the world of SQL! While we’ve only scratched the surface of what’s possible with this powerful language, it is hoped that this brief introduction has given you a taste of the simplicity and power of SQL. Happy querying!