Which of the following relational algebra commands or combination of commands is capable of retrieving a single cell value from a relation?
A) Select.
B) Project.
C) Join.
D) Select and Project.
E) Select, Project, and Join.

Question

Quizplus · Accepted Answer

The Select command is used to select certain rows from a relation based on a certain condition or criteria. The Project command is used to select certain columns from a relation. Neither of these commands alone is capable of retrieving a single cell value from a relation. However, by combining the Select and Project commands, it is possible to retrieve a single cell value. The Select command is used to select the row that contains the desired cell value, and the Project command is used to select only the column that contains the cell value. Therefore, the correct answer is D.

Which of the Following Relational Algebra Commands or Combination of Commands