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PHP and MySQL Interview Questions with Answers

1.Difference Between Char and Varchar data type?

  • CHAR Data Type is a Fixed Length Data Type. It can be any value from 0 to 255 bytes.Uses static memory allocation.
    For example, if you declare a variable/column of CHAR (10) data type, then it will always take 10 bytes irrespective of whether you are storing 1 character or 10 character in this variable or column. And in this example, as we have declared this variable/column as CHAR(10), so we can store max 10 characters in this column.
  • On the other hand, VARCHAR is a variable length Data Type.Maximum lengths can range from 0 to 255 bytes (before MySQL 5.0.3) or from 0 to 65,535 bytes in later versions.Uses dynamic memory allocation.
    For example, if you declare a variable/column of VARCHAR(10) data type, it will take the number of bytes equal to the number of characters stored in this column. So, in this variable/column, if you are storing only one character, then it will take only one byte and if we are storing 10 characters, then it will take 10 bytes. And in this example, as we have declared this variable/column as , VARCHAR(10) so we can store max 10 characters in this column.

2.What all are the Mysql Storage Engines?

  • InnoDB-
    InnoDB is the most widely used storage engine with transaction support. It is an ACID compliant storage engine. It supports row-level locking, crash recovery and multi-version concurrency control. It is the only engine which provides foreign key referential integrity constraint. Oracle recommends using InnoDB for tables except for specialized use cases.
  •   MyISAM-
    MyISAM is the original storage engine. It is a fast storage engine. It does not support transactions. MyISAM provides table-level locking. It is used mostly in Web and data warehousing.
  • Memory-
    Memory storage engine creates tables in memory. It is the fastest engine. It provides table-level locking. It does not support transactions. Memory storage engine is ideal for creating temporary tables or quick lookups. The data is lost when the database is restarted.
  • CSV-
    CSV stores data in CSV files. It provides great flexibility because data in this format is easily integrated into other applications.
  • Merge-
    Merge operates on underlying MyISAM tables. Merge tables help manage large volumes of data more easily. It logically groups a series of identical MyISAM tables, and references them as one object. Good for data warehousing environments.
  • Archive-
    Archive storage engine is optimised for high speed inserting. It compresses data as it is inserted. It does not support transactions. It is ideal for storing and retrieving large amounts of seldom referenced historical, archived data.
  • Blackhole-
    The Blackhole storage engine accepts but does not store data. Retrievals always return an empty set. The functionality can be used in distributed database design where data is automatically replicated, but not stored locally. This storage engine can be used to perform performance tests or other testing.
  • Federated-
    Federated storage engine offers the ability to separate MySQL servers to create one logical database from many physical servers. Queries on the local server are automatically executed on the remote (federated) tables. No data is stored on the local tables. It is good for distributed environments.

3.$a=3,$b=7 swap values of these two variable without using third variable.
$a = $b – $a;
$b = $b – $a;
$a = $b + $a;
4.Difference between joins and union?
5.What all types of joins are there?
6.Difference between minified js jquery.min.js and jquery.js ?
7.Latest versions of Mysql,PHP,Codeigniter.
8.Differences between older and newer versions.
9.Difference between echo and print?
10.CURL functions?
11.How to set unlimited upload_max_filesize?
12.libarary/helper for xss_clean?
13.Difference between library and helper?
14.Get last executed query and insert id in MySQL with PHP/CodeIgniter.
$this->db->last_query();
$this->db->insert_id();

sample htaccess file

Sample htaccess file

<Limit GET POST>
order allow,deny
SetEnvIf Remote_Addr ^10\.87\. ban
#allow from 10.87.63.0/8
allow from env=allow
deny from env=ban
</Limit>
#https://www.countryipblocks.net/block-specific-ips-from-your-allow-list-using-setenvif

<IfModule mod_rewrite.c>
  RewriteEngine on
  RewriteRule ^test$ https://google.co.in
  #RewriteRule .* https://google.co.in
    #RewriteRule ^abc/([a-z]*)/([0-9]*)$ xyz.php?name=$1&id=$2 [NC,L,QSA]
    #RewriteCond %{HTTP_HOST} ^reporting.soc.saint-gobain.net [NC] 
    #RewriteCond %{SERVER_PORT} 80 RewriteRule ^(.*)$ https://domain.com/$1 [R,L]
</IfModule>

 

 

php debug performance script

Php Script to check bugs and performance:
<?php

/** Error reporting */
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
date_default_timezone_set('Asia/Kolkata');
define('EOL',(PHP_SAPI == 'cli') ? PHP_EOL : '<br />');
date_default_timezone_set('Asia/Kolkata');

echo date('H:i:s') , " Program Started" , EOL;


// Echo memory peak usage
echo date('H:i:s') , " Peak memory usage: " , (memory_get_peak_usage(true) / 1024 / 1024) , " MB" , EOL;
// Echo done
echo date('H:i:s') , " Program End" , EOL;

?>

 

Core Java Assignment

Classes and Objects
1. Create class Rectangle
a) data members
– length
– breadth
b) methods
– setDimensions
– area
– perimeter

2. Create class Cube
a) data members
– length
– breadth
– height
b) methods
– setDimensions
– volume

3. Create class Worker
a) data members
– wages
– wdays
b) methods
– setData
– payment

Method Overloading

1. Create class Box
a) data members
– length
– breadth
– height
b) methods
– setDimensions(3 args)
– setDimensions(1 arg)
– volume

Method Returning Value
1. WAP to find total payment of two employeesCreate
Create class Worker
a) data members
– wages
– wdays
b) methods
– setData
– int payment

Constructors
1. Create class Circle and initialize radius using a default constructor
2. Create class Circle and initialize radius using parameterized constructor
3. Create class Circle and define two constructor default and parameterized (Constructor overloading)

Static data members and member functions
1. Create a class Circle and find its area
a) data members
– int radius
– static double pi
b) methods
– area

2. Create a class Bank Account and find interest
a) data members
– int account_number
– int balance
– static double interest_rate
b) methods
– interest (balance * interest_rate * no_of_period / 100.0)
– changeRate (change interest_rate)

How to run linux commands on windows

    1. Cygwin is a Unix-like environment and command-line interface for Microsoft Windows.
      Cygwin provides native integration of Windows-based applications, data, and other system resources with applications, software tools, and data of the Unix-like environment.
      Thus it is possible to launch Windows applications from the Cygwin environment, as well as to use Cygwin tools and applications within the Windows operating context.

      Official Site: https://www.cygwin.com/

       

    2. git bash is a shell where: the running process is sh.exe (packaged with msysgit, as share/WinGit/Git Bash.vbs)
      git is a known command$HOME is defined

      Official Site: https://git-scm.com/

  • How to install cygwin on Windows

How to enable ssh login to windows using cygwin

rsync on windows os

rsync: Failed to exec ssh: No such file or directory(2) on windows

nstalling cwrsync, you are likely to get this error  when you try to run this sample command from the command line.

rsync  -avz  -e  ssh ycsoftware@google.com:/home/ycsoftware /cygdrive/z/ycsoftware/

“rsync: Failed to exec ssh: No such file or directory(2)” cwrsync

The reason you are getting this is because for some reason rsync is not able to find the path to the ssh.exe file. You should change it to something like this:

C:/cygwin64/bin/rsync.exe -ar . /cygdrive/c/xampp/htdocs/test2/

Ref: http://ycsoftware.net/rsync-failed-to-exec-ssh-no-such-file-or-directory2-on-windows/