Relational Algebra Flashcards
A set of mathematical principles that form the basis for manipulating relational table contents; the eight main functions are SELECT, PROJECT, JOIN, INTERSECT, UNION, DIFFERENCE, PRODUCT, and DIVIDE.
Relational Algebra
A container (variable) for holding relation data (not the relation itself). It consists of a heading, which is made of the names of attributes, and a body, which is the data.
Relational Variable or “relvar”
A unary relational operator that yields values for all rows found in the table that satisfy a given condition. All attributes are included in the result.
SELECT or RESTRICT represented by the Greek letter sigma sigma (σ).
A property of relational operators that permits the use of relational algebra operators on existing tables (relations) to produce new relations.
Closure
A unary operator that will return only the attributes requested in the order requested. All rows are returned.
PROJECT, denoted by the Greek letter pi (π).
Combines all rows from two tables, excluding duplicate rows. The tables must have the same attribute characteristics.
UNION
Two or more tables that have the same number of columns and the corresponding columns have compatible domains.
Union compatible
An operator used to yield only the rows that are common to two union-compatible tables.
INTERSECT, denoted by the upside down U symbol
An operator used to yield all rows from one table that are not found in another union-compatible table.
DIFFERENCE, denoted by the minus symbol.
An operator that yields all possible pairs of rows from two tables
PRODUCT, denoted by the multiplication symbol “x”
A type of operator used to yield rows from two tables based on criteria.
JOIN, denoted by the symbol ⋈.
A relational operation that yields a new table composed of only the rows with common values in their common attribute(s).
natural join
Columns that are used in the criteria of join operations. The join columns generally share similar values.
join columns
