Yes, I have used union and union all in a project before. The scenario was when I was working on a data analysis project for a client. The client had multiple datasets that contained different sets of data, but all the datasets were related to the same topic. The datasets had different structures, and the data was not always consistent. To analyze the data, I had to combine the datasets into a single table. I used the union and union all functions to do this. The union function combines the datasets and removes any duplicates, while the union all function combines the datasets and keeps any duplicates. I used the union function when I wanted to ensure that there were no duplicate records in the combined table. This was important because I needed to have a unique record for each data point in the table. I used the union all function when I wanted to keep all the records, even if there were duplicates. This was useful when I wanted to see how many times a certain data point appeared in the datasets. To implement the union and union all functions, I used SQL queries to select the data from each dataset and then used the union or union all function to combine the data. I then created a new table in the database to store the combined data. Overall, using the union and union, all functions allowed me to easily and efficiently combine the datasets and analyze the data. This question is one of the common JOIN SQL interview questions, be ready to tackle it.