Free eBooks for Beginners

SQL is a powerful and widely used language in data analysis, and understanding how to use its various functions is crucial to effectively working with databases. One of these functions is the UNION and UNION ALL operator. These operators allow you to combine the results of two or more SELECT statements into a single result set. In this article, we will explore the basics of using UNION and UNION ALL in SQL.

UNION

The UNION operator is used to combine the results of two or more SELECT statements into a single result set. The SELECT statements used in a UNION operation must have the same number of columns, with the same data types in the same order. The UNION operator eliminates duplicates from the results, meaning that if two SELECT statements return the same row, it will only appear once in the final result set.

For example, if you have two tables, “employees” and “managers”, and you want to combine the results of a SELECT statement on each of these tables into a single result set, you can use the UNION operator as follows:

SELECT first_name, last_name 
FROM employees 
UNION 
SELECT first_name, last_name 
FROM managers;

The result of this statement will be a single result set containing the first and last names of all employees and managers, with any duplicates removed.

UNION ALL

The UNION ALL operator is similar to the UNION operator, but it does not eliminate duplicates from the results. This means that if two SELECT statements return the same row, it will appear in the final result set as many times as it appears in the SELECT statements.

For example, if you have two tables, “employees” and “managers”, and you want to combine the results of a SELECT statement on each of these tables into a single result set, including any duplicates, you can use the UNION ALL operator as follows:

SELECT first_name, last_name 
FROM employees 
UNION ALL 
SELECT first_name, last_name 
FROM managers;

The result of this statement will be a single result set containing the first and last names of all employees and managers, with any duplicates included.

In conclusion, the UNION and UNION ALL operators are a valuable tool for combining the results of multiple SELECT statements into a single result set. Understanding when to use each operator, and how to use them effectively, is an important part of working with SQL in a data analyst role.

SQL for Beginners and Data Analyst – Chapter 24: UNION / UNION ALL

Loading...

Taking too long?

Reload document

| Open in new tab

Download PDF [117.92 KB]

Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause. The information presented here could also be found in public knowledge domains.