Relational set operators

Question 1

SELECT

Answer 1

σ A (R)

ex: σ Length_mRNA >1500
^ Length_mRNA < 2000 (GENE)

This translates to “select from gene table the attribute Length_mRNA that is between 1500 and 2000”.

Question 2

PROJECT

Answer 2

a form of restriction which restrict the subset of
columns that will be returned

ex: π gene_symbol, location (GENE)

This translates to “project from gene table the attributes gene_symbol and location”.

Question 3

JOIN

Answer 3

|X| (GENE.GeneID = EXPRESSION.GeneID)

Question 4

INTERSECT

Answer 4

returns those rows common to the specified relations

Symbol: ∩

Example:
σ Length_mRNA = 2000 (GENE)
∩
σ ExpressionLevel > 5 (EXPRESSION)

SELECT * FROM A
INTERSECT
SELECT * FROM B

This is similar to INNER JOIN

Question 5

UNION

Answer 5

combines all of the rows from the
specified tables BUT excludes duplicates

Symbol: ∪

Example:
σ Length_mRNA = 2000 (GENE)
∪
σ ExpressionLevel > 5 (EXPRESSION)

SELECT * FROM A
UNION
SELECT * FROM B

Question 6

DIFFERENCE

Answer 6

turns all rows from
one table that are NOT in another

Symbol: -

Example:
σ Length_mRNA = 2000 (GENE)
−
σ ExpressionLevel > 5 (EXPRESSION)

SELECT * FROM A
EXCEPT
SELECT * FROM B

Question 7

operators used

Answer 7

+, -, =, <, >, /=, <=,>=

Question 8

and, or, not

Answer 8

^, ∨, ¬