October 13, 2018

Sreekanth B

Cognizant MySQL Most Frequently Asked Latest Interview Questions Answers

How to take MYSQL database backup?

To take the database backup use the following syntax:
mysqldump --add-drop-table -u [username] -p[password] [database] > [backup_file]

This command will take the database backup by knowing the username and password for the database connection and dropping any table which is being deleted or not in use. It is always a good practice to take the backup of mysql as it contains all the database information that a user can access. While using the command keep a note that there should not be any space between –p switch and password, if there is then you will get a syntax error.

Write a command with which MySQL table can be repaired

The command syntax with which mysql table can be repaired is as follows:
REPAIR TABLE tablename;
REPAIR TABLE tablename QUICK;
REPAIR TABLE tablename EXTENDED;

The command will just do as it says repair a specified table, but if QUICK or EXTENDED is used then the meaning of it changes. In case of QUICK it will repair only the index tree, whereas in case of EXTENDED it will create index row by row and repair it.

What are the different tables present in MySQL?

There are many tables that remain present by default. But, MyISAM is the default database engine used in MySQL. There are five types of tables that are present:

1. MyISAM
2. Heap
3. Merge
4. INNO DB
5. ISAM
Cognizant MySQL Most Frequently Asked Latest Interview Questions Answers
Cognizant MySQL Most Frequently Asked Latest Interview Questions Answers

What does the file with the extension: frm, myd, and myi contain?


MySQL default table type is MyISAM, where there are three kind of files that are stored inside MyISAM. The file names begin with the table name and have the extensions such as frm, myd and myi. The explanation of each file is given below:

.frm file consists of the table definition that are stored in the database
.myd is an extension that is used by a data file.
.myi is an extension that is used by index file.

What is the difference between MYSQL and SQL?

- SQL is known as standard query language, as the name implies it is the language which is used to interact with the database like MySQL.

- MySQL is a database that store various types of data and keep it safe. A PHP script is required to store and retrieve the values inside the database.

How database are managed?

Database is a collection of data and it is managed by a database server, which is a special program that is also known as MySQL database server. Application that you create usually communicates with the database server in the language which it can understand; mostly SQL language is used for communication. Database server in return interacts with the web server on same server or computer. Database server and web server result in the data which is being shown on the web.

What is required to create MYSQL database?

To create MySQL databse the first component which has to be present is a database server on which the queries of database will run and software tool through which you can access the applications. It also requires PHP scripts for communicating with the database using SQL commands.

What do you understand by MYSQL terminal?

MySQL terminal is used as a command line interface in many operating system. It provides a way to access the database and other resources using the SQL commands that are interpreted by the MySQL database server.

Why phpMyAdmin is used for MYSQL?

PhpMyAdmin is a very popular and easy to use GUI tool that can allow SQL commands to be run to create database, create tables, insert data and retrieve it. It provides a web based interface to the user for the ease of use. phpMyAdmin allows user to manage everything from one place and no other installation is required in the computer after this.

Write a query to create a database and a table?

MySQL comes up with some default database that can be used as a base to create a new one. The command that is used to create a new database is as follows:
CREATE DATABASE SQL command

The command has to be written in MySQL terminal. This command will create a new database and then you can create new tables and include data in it.

How can you make a database as your current database?

After making a database the first thing which has to be done is to create a table inside the database to test the new database that is being created. The command which is used to do that is:
USE aliendatabase;

This command allows us to make a database which is not a current database as my current. I have to just use the USE variable and the name of the database and it will become active for use.

What is the difference between a database and a table?

There is a major difference between a database and a table. The differences are as follows:

1. Tables are a way to represent the division of data in a database. Whereas, database is a collection of tables and data.
2. Tables group the data in relation with each other and create a dataset; this dataset will be used in the database. The data which are stored in the table in any form is a part of the database, but opposite is not true.

Is the syntax correct? Explain the meaning of the syntax given below

$dbc = mysqli_connect('data.aliensabductedme.com', 'owen', 'aliensrool', 'aliendatabase');

Yes the syntax is correct and this query is getting used to connect the database with a PHP script. PHP uses three functions to communicate with MySQL database. The three functions are:

mysqli_connect(), mysqli_query(), and mysqli_close().

mysqli_connect() and mysqli_query() are used to connect to mysql database and issue a query to the database. mysqli_query() is also used to retrieve the string or any other data from the database. Mysqli_close() is used to close a connection with the database.

How to connect a PHP script with the MySQL database?

PHP script can be connected with MySQL database by using the function called as mysqli_connect() function. You need to provide the information related to your location, username and password to the server to get permission to interact with the MySQL database server. When database name will be asked provide the name and it will connect you to the database.

What is the difference between truncate and delete?

Delete command is used to delete data from a table for example Remove emails where we write a script to delete the customer’s data. It deletes the rows of data from a table. The syntax of it as follows:
DELETE FROM table_name

Whereas, truncate is very dangerous command and should be used carefully as it deletes every row from a table. The syntax of it as follows:
TRUNCATE TABLE "table_name"

How important is to list the column names when doing an INSERT?

It is not important to list the column names when doing using an INSERT command as you can provide the column information and values in the table in the same order in which they appear in the table structure. It is safer and convenient way to specify the column names as it will keep the count of the column you are visiting.

Where’s database data actually stored? Is there a way to see the files which are stored?

Database data is usually get stored in the computer hard-disk and you can manage the data by the database program like MySQL and phpAdmin. The files can be seen but database files remain in binary format so it can be opened and read but, you have to put extra effort to understand it. SQL is given for the purpose of interacting with the database and read the database and retrieve the information out of it.

Why to use CHAR instead of VARCHAR in the database?

CHAR is much more accurate and efficient to use. CHAR doesn’t have to keep a count of the variable length. It is more efficient when you have to use it for a text column which is of an exact length. Char is used for the data which are fixed, but VARCHAR is used for data like password, which are variable.

What Is Mysql Default Port Number?

MySQL default port number is 3306.

What Is Regexp?

REGEXP is a pattern match using regular expression. Regular expression is a powerful way of specifying a pattern for a complex search.

How Many Columns Can You Create For An Index?

You can create maximum of 16 indexed columns for a standard table.

What Is The Difference Between Now() And Current_date()?

NOW() command is used to show current year, month, date with hours, minutes and seconds while CURRENT_DATE() shows the current year with month and date only.

What Is A Trigger In Mysql?


A trigger is a set of codes that executes in response to some events.

What Is The Difference Between Heap Table And Temporary Table?

Heap tables:

Heap tables are found in memory. They are used for high speed storage on temporary basis. They do not allow BLOB or TEXT fields.
Heap tables do not support AUTO_INCREMENT.
Indexes should be NOT NULL.
Temporary tables:

The temporary tables are used to keep the temporary data. Sometimes it is very useful in cases to keep temporary data. Temporary table is deleted after current client session terminates.
Main differences:

The heap tables are shared among clients while temporary tables are not shared.
Heap tables are just another storage engine, while for temporary tables you need a special privilege (create temporary table).

What Is The Difference Between Float And Double?


FLOAT stores floating point numbers with accuracy up to 8 places and allocates 4 bytes, on the other hand DOUBLE stores floating point numbers with accuracy up to 18 places and allocates 8 bytes.

What Are The Advantages Of Mysql In Comparison To Oracle?

MySQL is a free, fast, reliable, open source relational database while Oracle is expensive, although they have provided Oracle free edition to attract MySQL users.
MySQL uses only just under 1 MB of RAM on your laptop while Oracle 9i installation uses 128 MB.
MySQL is great for database enabled websites while Oracle is made for enterprises.
MySQL is portable.

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