Question

1. Define the term tuple, attribute and relation.
2. Discuss the difference between a relation and a table.
3. What constitutes union compatibility?
4. What is a Cartesian Product operation?
5. When must a GROUP BY clause be used in a query?
6. Explain functional dependency between two attributes?

paraphrase please, Do not copy-paste, please.

Answer 1

• A tuple is a row in a table or it is a record of a table or it is a ordered set of values. It represents some facts that corresponds to real world entity. An attribute is the columns in a table. All the values under an attribute is derived from an appropriate domain. Set of tuples or rows are known as a relation .
• The main difference between a table and a relation is that, a table is a collection of values which can contain duplicate values. Relation can also be called as a table, but it is a set of values that are un-ordered and there should not be any duplicate values.
• For two relations to be union compatible, they should have same number of attributes and similar attributes should belong to same domain (i.e., domain of jth attribute of a relation and domain of jth attribute of another relation should be same).
• Cartesian Product combines the tuples of a relation with the tuples of another relation. It also known as cross product.
• A GROUP BY clause is mainly used with a SELECT statement to group rows that have identical values( it will group all the identical rows and a return a single row).
• A set of attributes X functionally determines a set of attributes Y if the value of X determines a unique value for Y( i.e., one attribute uniquely determines another attribute). It is a constraint between two attributes.