Learn SQL
UNION
41.1
Lesson

UNION

Let’s say we want to display all the person names available to us, namely all the names of students, and all the names of authors, in a single result, under a single column.

In this case, we need to include data from two entirely different queries:

  1. SELECT name FROM students

  2. SELECT name FROM authors

and present them together in a single column.

For such a use case, SQL provides a combination clause called UNION, which helps display data of different types together, from results of two or more queries.

Notice that the results contain 35 rows of names (25 students + 10 authors).

Another key thing to notice about UNIONs is, the number of columns from each query that constitutes a union, should be equal. Go ahead and run the query below:

We see an error because the first query in the UNION results produces two columns, while the second one produces only one, which is not acceptable in a UNION.