How to Use SELECT and SELECT DISTINCT in SQL

Welcome back to our SQL tutorial series! In our previous article, we introduced SQL and its importance. Now, we’re going to dive deeper into two fundamental commands: SELECT and SELECT DISTINCT. These commands are crucial for retrieving data from your database. By the end of this tutorial, you’ll understand how to use them effectively with practical examples.

Understanding SELECT

The SELECT statement is the most basic and commonly used SQL command. It allows you to query and retrieve data from one or more tables. Let’s start with a simple example.

Example Table: employees

Let’s assume we have the following employees table:

Basic SELECT Statement

To retrieve all columns from the employees table, you use:

SELECT * FROM employees;

This command selects all columns (*) from the employees table and returns the following result:

Selecting Specific Columns

If you only want to retrieve specific columns, you can specify them in your SELECT statement:

SELECT name, position FROM employees;

This command selects only the name and position columns:

Understanding SELECT DISTINCT

The SELECT DISTINCT statement is used to remove duplicate values from your result set. This is particularly useful when you want to find unique values in a column.

Example with Duplicate Values

Let’s modify our employees table to include some duplicate values in the position column:

Using SELECT DISTINCT

To get a list of unique positions, you use the SELECT DISTINCT statement:

SELECT DISTINCT position FROM employees;

This command returns the following result:

Notice how Software Engineer and Data Analyst each appear only once in the result set, despite being duplicated in the original table.

Combining SELECT with Other Clauses

You can combine SELECT and SELECT DISTINCT with other SQL clauses to perform more complex queries. For instance, you might want to filter the results using the WHERE clause or sort them using the ORDER BY clause.

Filtering Results

To retrieve the names of employees who are Software Engineers, you use:

SELECT name FROM employees WHERE position = 'Software Engineer';

This returns:

Sorting Results

To retrieve all employees’ names and positions, sorted by their names, you use:

SELECT name, position FROM employees ORDER BY name;

This returns:

Conclusion

Understanding how to use SELECT and SELECT DISTINCT is essential for working with SQL databases. These commands allow you to retrieve and manipulate data efficiently, giving you the power to gain insights and make informed decisions based on your data.

Stay tuned for our next tutorial, where we’ll explore more advanced SQL concepts and commands. Happy coding!