Should this be selection or projection
I have am learning relational algebra. I have a table, Staff(name,salary,position) Now a question states, List all the managers with salary >25,000 Now the correct answer is, selection position = manager ^ salary >25000(staff) But I was thinking that it was, projection position = manager ^ salary >25000(staff) As we are selecting a particular attribute in the table and not selecting all the attributes. Please guide. Thanks
You want to "list all the managers", that means "select a number of rows". You are not "selecting a particular attribute", but you are filtering on a particular attribute (to select a row). Projection would be "list all the managers' names and salaries". In terms of SQL: Selection is the WHERE clause Projection is the list of columns in the SELECT clause
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