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Why does the relation created as result of a Projection operation on a relation that includes the primary key not contain fewer tuples than those in the source relation?

QUESTION:

Why does the relation create a result of a Projection operation on a relation that includes the primary key not contain fewer tuples than those in the source relation?

 

SOLUTION

 

There are no duplicate tuples to eliminate since the value of the attribute(s) that constitute the primary key is unique in the source relation.

With which of the four types of constraints in Exercise 4 is a requirement that an attribute not contain a null value associated?

QUESTION:

With which of the four types of constraints in Exercise 4 is a requirement that an attribute not contain a null value associated?

 

SOLUTION

 

A not null constraint is associated with a CHECK clause.

What is the difference between a column-level constraint and a row-level constraint?

QUESTION:

What is the difference between a column-level constraint and a row-level constraint?

 

SOLUTION

 

A column-level constraint is imposed on a single column in the table while a row-level constraint is imposed on a set of columns in the table.

What are the minimum elements that must be included in the CREATE TABLE statement in defining the structure of a table?

QUESTION:

What are the minimum elements that must be included in the CREATE TABLE statement in defining the structure of a table?

 

SOLUTION

 

The CREATE TABLE statement must contain the table name, the names of the columns in the table, and the data type for each column.

What are the undesirable functional dependencies in the relation instance of the STUCLASS relation schema shown in Exercise 6?

QUESTION:

What are the undesirable functional dependencies in the relation instance of the STUCLASS relation schema shown in Exercise 6?

 

SOLUTION

 

Snum → Sname, Snum → Major, Cname → Time, Cname → Room, Time → Cname, Time → Room.