Add Columns If they exist

Hi,

1. This is some dummy data I created in excel but my query returns something similar to this kind of scenario 

2. Transform Data > Select Fruit Column > Pivot Column > Values Column (Quantity) > Aggregate Function (Sum).It creates something like this below

3. Now I need to create another column that adds all the quantities related to melons category. For ex sometimes the query may return only Watermelon and Muskmelon and sometimes maybe just Honeydew melon and sometimes maybe Honeydew and Muskmelon. How to create total column by checking if a column exists and then add? However I know for sure the query returns only four fruits related to melons (i.e they are hardcoded)