State the difference between the following:

Question

a. Union and Intersection
b. product and join
c. selection and projection

Answer 1

a. The Union operation on two tables returns all rows from both the tables,
but it does not repeat the duplicate rows. The Intersection operation on
two table returns rows that exist in both tables involved.
b. A product of two table matches every row from the first table to each
and every row in the second table. The join operation on two tables joins
rows from two tables based on a common attribute, and the rows with
same common attribute value are joined to each other.
c. The Selection operation on a table returns rows that satisfy the supplied
criteria. The projection operation returns the attributes specified from a
table.