Solution:
Relational Algebra defines the theoretical foundation of manipulating
table content using the eight relational operators:
SELECT, PROJECT, JOIN, INTERSECT, UNION, DIFFERENCE, PRODUCT,
AND DIVIDE.
The relational operators have the property of closure that is applying
operators on relations produce relations.
1. SELECT, also known as RESTRICT, yields values for all the rows
found in a table that satisfy a given condition. SELECT yields a
horizontal subset of a table.
2. PROJECT yields all values for selected attributes. PROJECT yields a
vertical subset of a table
3. UNION: combines all rows from two or more tables, excluding
duplicate rows. In order to be used in a UNION, the tables must
have the same attribute characteristics, that it the attributes and
their domains must be compatible. When two or more tables
share the same number of columns and when their corresponding
columns share the same or compatible domains, they are said to
be union-compatible.
4. INTERSECT: yields only the rows that appear in both tables. As
with UNION, the tables must be union-compatible to yield valid
results.
This is the right answer.