Sometimes there are situations when it is desirable to collect multiple result sets in a single output. Merge Result Set is used to specify what result sets should be merged, their order in the output and if the SQL used to produce each result set should be included.
The following screenshot shows four result sets, right-click one of them and select Merge Result Sets in the menu: 
In the merge window all available result sets are listed. Use the checkbox in front of each result set to control whether it should be included or not. To change the order select a row and drag it up or down.
The result of the merge operation is available in a new tab and this is the result as specified in the merge setup window previously: