Mastering DBMS Concepts

What is the purpose of the COUNT() function in SQL?

• To retrieve unique values from a column.

• To calculate the average value of a column.

• To sort the rows in a result set.

• To count the number of rows in a result set.

How do you retrieve unique values from a column in SQL?

• SELECT ALL column_name FROM table_name;

• SELECT UNIQUE column_name FROM table_name;

• SELECT DISTINCT column_name FROM table_name;

• SELECT column_name FROM table_name GROUP BY column_name;

Explain the difference between INNER JOIN and OUTER JOIN in SQL.

• INNER JOIN can only be used with two tables; OUTER JOIN can be used with multiple tables.

• INNER JOIN and OUTER JOIN are the same and can be used interchangeably.

• INNER JOIN returns matched records only; OUTER JOIN returns all records from one table and matched records from the other.

• INNER JOIN returns all records from both tables; OUTER JOIN returns only unmatched records.

What is the role of the GROUP BY clause in SQL?

• The GROUP BY clause sorts the rows in ascending order.

• The GROUP BY clause is used to delete duplicate rows from a table.

• The GROUP BY clause groups rows that have the same values in specified columns into summary rows.

• The GROUP BY clause creates new tables based on column values.

Define the term 'relation' in the context of relational algebra.

• A relation is a single tuple with unique attributes.

• A relation is a collection of unrelated data points.

• A relation is a graphical representation of data without structure.

• A relation is a set of tuples sharing the same attributes, represented in a tabular format.

What is the primary purpose of relational calculus?

• To create database schemas.

• To specify queries in a declarative manner.

• To manage user permissions.

• To optimize query performance.

List and explain the types of constraints in the relational model.

• Default Key

• Composite Key

• Index Key

• The types of constraints in the relational model are: Primary Key, Foreign Key, Unique, Not Null, and Check.

What is a primary key and why is it important?

• A primary key is a visual representation of data in a database.

• A primary key is a type of database index that speeds up queries.

• A primary key is a unique identifier for records in a database, crucial for data integrity and efficient retrieval.

• A primary key is a field that can contain duplicate values in a database.

How does a foreign key differ from a primary key?

• A primary key can link to multiple tables; a foreign key cannot.

• A primary key uniquely identifies records; a foreign key links to a primary key in another table.

• A primary key is used for indexing; a foreign key is not related to indexing.

• A foreign key is always unique; a primary key can be duplicated.

What is the significance of the DISTINCT keyword in SQL?

• The DISTINCT keyword is used to sort the result set.

• The DISTINCT keyword adds additional columns to the result set.

• The DISTINCT keyword is used to group rows in the result set.

• The DISTINCT keyword is significant because it eliminates duplicate rows from the result set.