Computer Science Test - 7

The correct answer is option 2.

Concept:

The CHECK constraint is used to restrict the range of values that may be entered into a column. When we define a CHECK constraint on a column, only particular values are allowed for that column.

• When a table has a CHECK constraint, it might limit the values in specific columns based on the values in other columns in the row.
• A check constraint is a rule that specifies the permissible values in one or more columns of each row of a base table.

Example:

The following SQL creates a CHECK constraint on the "Age" column when the "student" table is created. The CHECK constraint ensures that the age of a student must be 18, or older:

CREATE TABLE student (

ID int NOT NULL,

LastName varchar(255) NOT NULL,

FirstName varchar(255),

Age int, CHECK (Age>=18) );

Hence the correct answer is the CHECK constraint.

The correct answer is option 3.

Concept:

In SQL, we can temporarily rename a table or a column by giving it another name known as Alias. Table aliases are used to rename a table in a specific SQL statement. The renaming is only a temporary change, and the actual table name in the database remains unchanged.

Syntax: The following is the basic syntax for a table alias.

SELECT column1, column2....

FROM table_name AS alias_name

WHERE [condition];

Syntax: The following is the basic syntax for a column alias.

The correct answer is "option 4".

CONCEPT:

GROUP BY clause: The GROUP BY clause in SQL is used to group the rows having the same values.

HAVING clause: HAVING clause in SQL is used instead of WHERE with an aggregate function.

EXPLANATION:

Here, 

Group by grade will produce the following table:

The SQL query "select avg(salary) from EMP group by grade having grade="E4" " will produce the output average salary of employees who belong to grade "E4".

Final output:

Hence, the correct answer is "option 4".

Relational Data Base:

• A relational database is a collection of data items with pre-defined relationships between them.
• These items are organized as a set of tables with columns and rows.
• Tables are used to hold information about the objects to be represented in the database.
• Each column in a table holds a certain kind of data and a field stores the actual value of an attribute.
• The rows in the table represent a collection of related values of one object or entity.
• Each row in a table could be marked with a unique identifier called a primary key, and rows among multiple tables can be made related using foreign keys.
• This data can be accessed in many different ways without reorganizing the database tables themselves.
• Examples: Popular examples of standard relational databases include Microsoft Access, Microsoft SQL Server, Oracle Database, MySQL, and IBM DB2. Cloud relational databases include Amazon Relational Database Service (RDS), Google Cloud SQL, IBM DB2 on Cloud, SQL Azure, and Oracle Cloud.

Concept:

• LIKE operator is used in a WHERE clause to search for a specified pattern in a column. 
• There are two wildcards often used in conjunction with the LIKE operator:

Syntax:

SELECT column_name1, column_name2 ... FROM table_name

WHERE  column_name LIKE '%Match'

OR

SELECT column_name1, column_name2 ... FROM table_name

WHERE  column_name LIKE '%Match%'

SQL command

SELECT ecode

FROM STUDENT

WHERE address LIKE '%MUMBAI%'

Return ecode from STUDENT table whose address part contains "INDIA" in any position.

NOTE:

address is a column in STUDENT table

Concept:

SQL stands for the structured query language. It is used to perform operations like creating, inserting, deleting and modifying the data in the database.

Explanation:

SQL count function:

It is used to count the number of records in the selected table. It is used with the SELECT statement.

Syntax: SELECT count(*) FROM table_name

Here  table_name is given as persons.

So, the number of records in the "persons" table can find out as :

SELECT count(*) FROM persons;

Answer: Option 2

Explanation: 

• A null value in a table is a value in a field that appears to be blank. A field with a Null value is a field with no value.
• A value of NULL indicates that the value is unknown. A value of NULL is different from an empty or zero value.
• No two null values are equal. Comparisons between two null values, or between a NULL and any other value, return unknown because the value of each NULL is unknown.

Since increment containing null value is ignored

Average = \(\frac{{18 + 16 + 17 + 17 +12\;}}{5} = 16\)

Average = 16

Important Points Tuple with null value is ignored and hence it is not included in the final calculation.

The correct answer is Relational Database Management System

Additional Information 

• Expansion of RDBMS is Relational Database Management System.
• It is a database management system which is based on the relational model.
• It was invented by E. F. Codd, in 1970.
• It is a set of programs which has all the features of DBMS (Database Management System) and it also helps to establish connections between tables.
• This software allows application systems to focus on the user interface, data validation, and screen navigation.

MySQL is an example of RDBMS.

The correct answer is DBMS.

Key Points

• A Database is an organized collection of data so that it can be easily accessed and managed.
• DBMS stands for Database Management System.
• A Database Management System (DBMS) is software designed to store, retrieve, define, and manage data in a database.
• Database Management System removes redundancy and Integrity.
• Database Management System reduces Application Development Time.
• DBMS follows the concepts of Atomicity, Consistency, Isolation, and Durability (normally shortened as ACID).
• DBMS supports a multi-user environment and allows them to access and manipulate data in parallel. 
• Types of DBMS Systems are:
  • Hierarchical Database
  • Network Database
  • Relational Database
  • Object-Oriented Database
• The three-schema architecture of DBMS:

• Some popular DBMS systems:
  • MySQL
  • Microsoft Access
  • Oracle
  • LibreOffice Base
  • Microsoft SQL Server

​Important Points 

• In 1960, Charles Bachman designed the first DBMS system.
• In 1970, Codd introduced IBM'S Information Management System (IMS)
• In 1976, Peter Chen coined and defined the Entity-relationship model also know as the ER model.
• In 1991, Microsoft ships MS Access, a personal DBMS and that displaces all other personal DBMS products.

​​​​ Additional Information 

• Operating System
  • ​An operating system acts as an intermediary between the user of a computer and computer hardware.
  • Operating systems were first developed in the late 1950s to manage tape storage.
  • The General Motors Research Lab implemented the first OS in the early 1950s for their IBM 701.
  • Operating System allows disk access and file systems Device drivers Networking Security.
  • Operating System Handling I/O operations.
  • Operating System has error detection and handling technic.
  • An Operating System is concerned with the allocation of resources and services, such as memory, processors, devices, and information. 
  • The Kernel is the central component of a computer operating system.
• ​Compiler
  • The compiler translates source code written in a high-level language into a set of machine-language.
  • Compilers are very large programs, with error-checking and other abilities.
  • The object code is machine code that the processor can perform one instruction at a time.
  • The first Autocode and compiler in the modern sense were developed by Alick Glennie in 1952.
  • John W. Backus at IBM introduced the first commercially available compiler, in 1957.