A database view is the results of which of the following operations?

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.

View Answer

Answer: D

Explanation: 1 The formal description of how a relational database operates. 2 The mathematics which underpin SQL operations.

A number of operations can be performed in relational algebra to build relations and operate on the data.

Five operations are primitives (Select, Project, Union, Difference and Product) and the other operations can be defined in terms of those five. A View is defined from the operations of Join, Project, and Select.

For the purpose of the exam you must remember the following terms from relational algebra and their SQL equivalent:

Tuple = Row, Entry

Attribute = Column

Relation or Based relation = Table

See the extract below from the ISC2 book: Each table, or relation, in the relational model consists of a set of attributes and a set of tuples (rows) or entries in the table. Attributes correspond to a column in a table. Attributes are unordered left to right, and thus are referenced by name and not by position. All data values in the relational model are atomic. Atomic values mean that at every row/column position in every table there is always exactly one data value and never a set of values. There are no links or pointers connecting tables; thus, the representation of relationships is contained as data in another table.

A tuple of a table corresponds to a row in the table. Tuples are unordered top to bottom because a relation is a mathematical set and not a list. Also, because tuples are based on tables that are mathematical sets, there are no duplicate tuples in a table (sets in mathematics by definition do not include duplicate elements).

The primary key is an attribute or set of attributes that uniquely identifies a specific instance of an entity. Each table in a database must have a primary key that is unique to that table. It is a subset of the candidate key.

Reference used for this question: Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 12262-12269). Auerbach Publications. Kindle Edition. and KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 46 and

http://db.grussell.org/slides/rel%20algebra%201ppt

NOTE: SQL offers three classes of operators: 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).

And the join operator allows the dynamic linking of two tables that share a common column value. The join operation is achieved by stating the selection criteria for two tables and equating them

with their common columns.

Most commercial implementations of SQL do not support a project operation, instead projections are achieved by specifying the columns desired in the output. This is why the Project operator is not well known as it is fading away from most databases.