A database view is the results of which of the following operations?
A.
Join and Select.
B.
Join, Insert, and Project.
C.
Join, Project, and Create.
D.
Join, Project, and Select.
Explanation:
SQL offers three classes of operators for creating views: select, project, and join.
The select operator serves to shrink the table vertically by eliminating unwanted rows (tuples).
The project operator serves to shrink the table horizontally by removing unwanted columns (attributes). Most
commercial implementations of SQL do not support a project operation, instead projections are achieved by
specifying the columns desired in the output.
The join operator allows the dynamic linking of two tables that share a common column value.
Incorrect Answers:
A: SQL offers three classes of operators for creating views: select, project, and join. However, modern
implementations of SQL do not support a project operation, instead projections are achieved by specifying the
columns desired in the output. Nevertheless, project is a SQL operator.
B: Insert is a SQL command used to insert data into a table. It is not used to output a view.
C: Create is a SQL command used to create a new database, table, view, or index. However, the data or output
of the view requires a select statement to shrink the table vertically by not showing unwanted rows, a project
operation that shrinks the table horizontally by not showing unwanted columns, and a join statement when data
from more than one table is required.http://db.grussell.org/section010.html
http://databasemanagement.wikia.com/wiki/Relational_Database_Model