How to Work with Unions in SQL
A common challenge in SQL is to combine the results from two or more selects. For example, we might want to list city name and state abbreviation on one report and then combine that output with a report on state name and state abbreviation. A union operation with solve this challenge!
To learn how work with unions in SQL, follow these steps:
- You'll need to setup the MySQL database tables. The instructions for the setup can be found in How to add comments in simple SQL selects. Follow steps 1 through 7 before proceeding to the next step.
- We can now write an a union in a SQL select.
- As mentioned above, let's write a union to display the city data combined with the state data. Execute this SQL select statement:
What we have are two select statements that are connected with the union keyword. Each select statement must display the same number of columns or expressions. Notice that I have included a literal expression on each select statement in order to make the output more readable (e.g., state data is identified as "State").