Learn SQL


Let’s say we want to display all the person names available to us. Person names means 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.