0 votes 0 votes Databases how er-to-relational this + – Saurabh Gupta 1 asked Sep 23, 2017 Saurabh Gupta 1 304 views answer comment Share Follow See all 4 Comments See all 4 4 Comments reply Manu Thakur commented Sep 23, 2017 reply Follow Share A and B both seem correct answers to me. the innermost query fetches records from the table works if there is an employee who works on some data base project. if it happens then the middle query will result empty because of Not Exists operator, and in turn outermost query will display eid for that employee. because pid is an unique key so i am assuming that there is only one database project.there should not be any difference between every and some database projects. 0 votes 0 votes Saurabh Gupta 1 commented Sep 23, 2017 reply Follow Share Iam not getting why employee having database project will be selected ? because of NOT EXISTS it has to be employee having not database as project will be selected please correct if iam wrong 0 votes 0 votes Manu Thakur commented Sep 23, 2017 reply Follow Share double negation! there are two NOT EXISTS operations 0 votes 0 votes Saurabh Gupta 1 commented Sep 23, 2017 reply Follow Share ok but double negation is for inner most query. –1 votes –1 votes Please log in or register to add a comment.