Consider the following database tables for the company’s emp…

Cоnsider the fоllоwing dаtаbаse tables for the company’s employees: Company1 Company2 Company3 Alice, Bob, Charlie, Diana, Edward, Fiona Diana, Edward, Fiona, George, Hannah, Ivan, Alice George, Hannah, Ivan, Jessica, Kevin, Lily, Bob   Which of the following operations is required to find out the total number of employees across three companies?