Premjith Sahyadhri

PHP Interview Questions

1. What is php? Who found it?

PHP (Hyper text Pre Processor) is a server side scripting language commonly used for web applications that allows web developers to create dynamic content that interacts with databases. Rasmus Lerdorf is the founder of php.

2. What is a web page?

A web page is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hyperlinks. Web pages frequently subsume other resources such as style sheets, scripts and images into their final presentation.

Web pages may be retrieved from a local computer or from a remote web server. The web server may restrict access only to a private network, e.g. a corporate intranet, or it may publish pages on the World Wide Web. Web pages are requested and served from web servers using Hypertext Transfer Protocol (HTTP).

Web pages may consist of files of static text and other content stored within the web server's file system (static web pages), or may be constructed by server-side software when they are requested (dynamic web pages). Client-side scripting can make web pages more responsive to user input once on the client browser.

3. How can you get the complete list of the PHP variables?

By looking at the output of the phpinfo() function.

4. What do you mean by Text Editors? And list the some PHP editors?

There are many text editors and Integrated Development Environments you can use to create, edit and manage PHP files. Notpad, notpad++, gedit, bluefish etc. Dream viewer and Net beans are the famous ide(s) used in the development of php.

5. Write the name of some databases that are currently supported to PHP?

MYSQL

Direct MS-SQL

Sybase

ODBC

oracle(OC 17 and OC 18)

mSQL

FrontBase

6. Write name of the web servers to which PHP supports?

Apache

Microsoft Internet Information Server(IIS)

personal web server

Netscape

7. How can I execute a PHP script using command line?

You can execute a PHP script by running the Command line interface program, in which you can enter the PHP script file as an argument. If the file is made for the web interface then it may not execute properly using command line. Command line allows faster execution of the statements and gives faster results.

8. How can we encrypt the password using PHP?

Crypt ( ) function is used to create one way encryption. It takes one input string and one optional parameter. The function look is defined as: crypt (input string, salt), where input string consists of the string which has to be encrypted and salt is an optional parameter.

<? Php

$password = crypt('mypassword');

print $password . “ is the encrypted version of mypassword”;

? >

9. What are different types of Runtime Errors in PHP?

There are three types of Runtime Errors in PHP. They are as follows:-

- Notices :

These are trivial, non-critical errors. that PHP encounters while executing a script - for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all - although you can change this default behavior.

- Warnings :

These are more serious errors - for example, attempting to include( ) a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.

- Fatal errors :

These are critical errors - for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP's default behavior is to display them to the user when they take place.

Internally, these variations are represented by twelve different error types

10. Define urlencode ( ) and urldecode( ) used in PHP?

urlencode ( ) returns the URL encoded version of given string. For URL encoding string values are used in the queries to be passed as URL. Whereas,

urldecode ( ) returns the URL decoded string (original string) which will be decoded by taking the already encoded string.

Example is as follows:

$discount ="10.00%";

$url = "http://domain.com/submit.php?disc=".urlencode($discount);

echo $url;

Output: "http://domain.com/submit.php?disc=10%2E00%25".

11. What is the difference between $message and $$message?

The only difference between $message and $$message is that, $message is a normal variable and $$message is variable to variable. The difference in functioning is shown below:

When declaring a variable in PHP the variable gets declared like this

$message //which is simply a variable

To store the data to assign the value to it we write like

$message= “ride”; //assigned the string to the variable

echo $message; // it will print the value ride

Whereas if you want to display the variable to variable then you use

$var = "Hello";

$message = "var";

echo $message; //print var

echo $$message; //print Hello.

12. What Is a Persistent Cookie?

Persistent cookie is a cookie which is permanently stored on user’s computer in a cookie file. They are used for tracking the user information of the users who are browsing from a very long time. They also have the drawbacks of being unsecure, as user can see the cookies which are saved on the computer.

. By default, cookies are created as temporary cookies which stored only in the browser's memory. When the browser is closed, temporary cookies will be erased. You should decide when to use temporary cookies and when to use persistent cookies based on their differences:

*Temporary cookies can not be used for tracking long-term information.

*Persistent cookies can be used for tracking long-term information.

*Temporary cookies are safer because no programs other than the browser can access them.

*Persistent cookies are less secure because users can open cookie files see the cookie values.

13. What is a PHP Session?

PHP session is not different from a normal session. It can be used to store information on the server for future use. PHP session allows you to store the user session, like their information on server for faster access and for later use like username, IP addresses, their actions etc. The information which is saved is temporary and can be deleted after the user is no longer active. Example of starting a PHP session is as follows:

<? php

Session start(); // start up your PHP session!

14. What is meant by PEAR in php? What is the purpose of it?

PEAR stands for "PHP Extension and Application Repository". As the name suggests, it gives advanced functionality to the PHP language and include many applications which can be used on fly.

The purpose of it is as follows:-

- Open source structured library for PHP users

- Code distribution and package maintenance system

- Standard style for code written in PHP

15. Is PHP a loosely Typed Language?. What is the difference between strongly typed and loosely typed language?

Yes, PHP is a loosely typed language.

In this type of language variable doesn’t need to be declared before their use. This language converts the data according to its given value.

Whereas, in strongly typed language first every type has to be declared (defined) then only it can be used.

16. Explain "GET" and "POST" methods ?.

Both the methods are used to send data to the server.

GET method - the browser appends the data onto the URL.

POST method - the data is sent as “standard input.”

17. Explain the "unlink" and "unset" functions.

unlink( ) function is for file system handling. It just deletes the file in context.

unset( ) function is for variable management. It makes a variable undefined

18. What is the default session time in PHP?

Until closing the browser.

19. How will you find out the value of current session id?

By using: session_id( )

20. How can we increase the execution time of a php script?

Default time allowed for the PHP scripts to execute is 30s defined in the php.ini file. The function used is set_time_limit (int seconds). If the value passed is ‘0’, it takes unlimited time.

21. What is zend engine? Explain the architecture of Zend engine with the diagram.

Zend engine is like a virtual machine and is an open source, and is known for its role in automating the web using PHP. Zend is named after its developers Zeev and Aandi. Its reliability, performance and extensibility has a significant role in increasing the PHP’s popularity. The Zend Engine II is the heart of PHP 5. It is an open source project and freely available under BSD style license.

Zend Engine is used internally by PHP as a complier and runtime engine. PHP Scripts are loaded into memory and compiled into Zend opcodes. These opcodes are executed and the HTML generated is sent to the client. The same is depicted above

22. What is the difference between Split and Explode?

In simple

Split - Splits string into array by regular expression.

Explode - Split a string by string

Split :

Returns an array of strings, each of which is a substring of string formed by splitting it on boundaries formed by the case-sensitive regular expression pattern.

If there are n occurrences of pattern, the returned array will contain n+1 items. For example, if there is no occurrence of pattern, an array with only one element will be returned. Of course, this is also true if string is empty. If an error occurs, split() returns FALSE.

Example :

<? Php // Delimiters may be slash, dot, or hyphen

$date = "04/30/1973";

list($month, $day, $year) = split('[/.-]', $date);

echo "Month: $month; Day: $day; Year: $year<br />\n";

spliti() - Split string into array by regular expression case insensitive

Explode :

explode ( string $delimiter , string $string , int $limit )

Returns an array of strings created by splitting the string parameter on boundaries formed by the delimiter.

If limit is set and positive, the returned array will contain a maximum of limit elements with the last element containing the rest of string.

If the limit parameter is negative, all components except the last -limit are returned.

If the limit parameter is zero, then this is treated as 1.

If delimiter is an empty string (""), explode() will return FALSE. If delimiter contains a value that is not contained in string and a negative limit is used, then an empty array will be returned, otherwise an array containing string will be returned.

Example :

<? php

$str = 'one|two|three|four';

print_r(explode('|', $str, 2)); // positive limit

print_r(explode('|', $str, -1)); // negative limit (since PHP 5.1)

The above example will output:

Array ( [0] => one,[1] => two|three|four )

Array ( [0] => one , [1] => two,[2] => three )

23. Explain the functionality of str_split( ) function in php

The str_split( ) function splits a string into an array.

Syntax :

str_split (string , length)

string - Required. Specifies the string to split

length - Optional. Specifies the length of each array element. Default is 1

Note:

If length is less than 1, the str_split () function will return FALSE.

If length is larger than the length of string, the entire string will be returned as the only element of the array.

Example 1

<? php

print_r (str_split ("Hello"));

The output of the code above will be:

Array ( [0] => H,[1] => e,[2] => l,[3] => l,[4] => o)

Example 2

<? php

print_r(str_split("Hello",3));

The output of the code above will be:

Array ( [0] => Hel,[1] => lo)

24. What is difference between developing website using Java and PHP?

Both technologies are used for dynamic websites development.

PHP is an interpreter based technology where as java is compiler based(usually JSP).

PHP is open source where as JSP is not.

Web sites developed in PHP are much more faster compared to Java technology

Java is a distributed technology, which means N tier application can be developed, where as PHP is used only for web development.

25. How can we know the number of days between two given dates using PHP?

The start date and end date can be first found as shown below:

$date1= strotime ($start_date);

$date2= strotime ($end_date);

$date_diff = (($date1)- ($date2)) / (60*60*24)

26. Different methods to pass data from one web page to another:

1. Store the data in a session variable. By storing the data, the data can be passed from one page to another.

2. Store data in a cookie: By storing data in a persistent cookie, data can be passed from one form to another.

3. Set the data in a hidden field and post the data using a submit button.

4. using get method

5. using post method

6. using javascript

27. $one = true; $two = null;

echo $a = isset($one) && isset($two);

echo $b = isset($one) and isset($two);

$a will out put false, while $b will out put true and what is the reason for this?

These are small aspects but very important a programmer must know. In the first phrase it uses “&&” operator to bind those two expressions which will give the expected answer. but the second one gives an unexpected answer where “and” operator is used.

The reason behind is the “higher precedence” between these 3 operators,

1. &&

2. =

3. and

In the first condition it will first check for the “&&” operation and then for the “=”

But in the second condition it will first look for the “=” operator and then for the “and”.

In order to fix this you can force the precedence by using parenthesis as follows,

echo $b = (isset($one) and isset($two));

28. Write a simple query to get the second largest value of a table column?

There are many ways that we can write this,

But the simplest way in mysql is,

SELECT * FROM country ORDER BY id DESC LIMIT 1, 1

And the following also are true

SELECT * FROM country ORDER BY id DESC LIMIT 1 OFFSET 1

select max(id) from country where id not in(select max(id) from country)

SELECT min(id) FROM (SELECT DISTINCT id FROM country ORDER BY id DESC LIMIT 2) AS t

29. How to reset/ destroy a cookie ?

Reset a cookie by specifying expire time in the past:

Example:

Setcookie ('Test',$i,time()-3600); // already expired time

Reset a cookie by specifying its name only

Example:

Setcookie ('Test');

30. Tools used for drawing ER diagrams ?.

1. Case Studio

2. Smart Draw

31. How can I know that a variable is a number or not using a JavaScript?

bool is_numeric( mixed var)

Returns TRUE if var is a number or a numeric string, FALSE otherwise.

The isNaN() function is used to check if a value is not a number.

Syntax

isNaN(number)

32. How can we submit from without a submit button?

Trigger the JavaScript code on any event ( like onSelect of drop down list box, onfocus, etc ) document.myform.submit(); This will submit the form.

33. What are the reasons for selecting LAMP (Linux, Apache, MySQL, Php) instead of combination of other software programs, servers and operating systems?

All of those are open source resource. Security of Linux is very more than windows. Apache is a better server that IIS both in functionality and security. Mysql is world most popular open source database. Php is more faster that asp or any other scripting language.

34. What are the features and advantages of OBJECT ORIENTED PROGRAMMING?

One of the main advantages of OO programming is its ease of modification; objects can easily be modified and added to a system there by reducing maintenance costs. OO programming is also considered to be better at modeling the real world than is procedural programming. It allows for more complicated and flexible interactions. OO systems are also easier for non-technical personnel to understand and easier for them to participate in the maintenance and enhancement of a system because it appeals to natural human cognition patterns. For some systems, an OO approach can speed development time since many objects are standard across systems and can be reused. Components that manage dates, shipping, shopping carts, etc. can be purchased and easily modified for a specific system.

35. How can we get second of the current time using date function?

$second = date("s");

36. How do you define a constant?

Via define() directive, like define ("MYCONSTANT", 100);

37. What are the differences between require and include, include_once, require_once()?

require_once ( ) and include_once ( ) are both the functions to include and evaluate the specified file only once. If the specified file is included previous to the present call occurrence, it will not be done again.

But require ( ) and include ( ) will do it as many times they are asked to do. The major difference between include ( ) and require ( ) is that in failure include ( ) produces a warning message whereas require ( ) produces a fatal errors.

If the file is not present, require ( ), calls a fatal error, while in include ( ) does not.

The include_once ( ) statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include ( ) statement, with the only difference being that if the code from a file has already been included, it will not be included again. It des not call a fatal error if file not exists. require_once ( ) does the same as include_once ( ), but it calls a fatal error if file not exists.

38. Would I use print "$a dollars" or "{$a} dollars" to print out the amount of dollars in this example?

In this example it wouldn’t matter, since the variable is all by itself, but if you were to print something like "{$a},000,000 mln dollars", then you definitely need to use the braces.

39. What are the different tables present in MySQL?

Total 5 types of tables we can create

1. MyISAM

2. Heap

3. Merge

4. INNO DB

5. ISAM

40. What is the functionality of the functions STRSTR() and STRISTR()?

string strstr ( string haystack, string needle ) returns part of haystack string from the first occurrence of needle to the end of haystack. This function is case-sensitive.

stristr() is idential to strstr() except that it is case insensitive.

For example:

strstr("user@example.com","@") will return "@example.com".

41. How do I find out the number of parameters passed into function?.

func_num_args () function returns the number of parameters passed in.

42. How do you call a constructor for a parent class?

parent::constructor($value)

43. What’s the special meaning of __sleep and __wakeup?

__sleep returns the array of all the variables than need to be saved, while __wakeup retrieves them.

44. For printing out strings, there are echo, print and printf. Explain the differences.

Echo :

echo is the most primitive of them, and just outputs the contents following the construct to the screen. We can pass multiple parameters to echo, like:

<?php echo 'Welcome ', 'to', ' ', 'techpreparations!'; ?>

and it will output the string "Welcome to techpreparations!"

Print :

print is also a construct (so parentheses are optional when calling it), but it returns TRUE on successful output and FALSE if it was unable to print out the string. Print does not take multiple parameters.

It is also generally argued that echo is faster, but usually the speed advantage is negligible, and might not be there for future versions of PHP.

Printf :

printf is a function, not a construct, and allows such advantages as formatted output, but it’s the slowest way to print out data out of echo, print and printf.

45. I am writing an application in PHP that outputs a printable version of driving directions. It contains some long sentences, and I am a neat freak, and would like to make sure that no line exceeds 50 characters. How do I accomplish that with PHP?

On large strings that need to be formatted according to some length specifications, use wordwrap ( ) or chunk_split ( ).

46. What’s the output of the ucwords function in this example?

$formatted = ucwords("TECHPREPARATIONS IS COLLECTION OF INTERVIEW QUESTIONS");

print $formatted;

What will be printed is TECHPREPARATIONS IS COLLECTION OF INTERVIEW QUESTIONS.

ucwords ( ) makes every first letter of every word capital, but it does not lower-case anything else. To avoid this, and get a properly formatted string, it’s worth using strtolower ( ) first.

47. What’s the difference between htmlentities() and htmlspecialchars()?

htmlspecialchars only takes care of <, >, single quote ‘, double quote " and ampersand. htmlentities translates all occurrences of character sequences that have different meaning in HTML.

48. How can we destroy the session, how can we unset the variable of a session?

session_unregister ( ) - Unregister a global variable from the current session

session_unset ( ) - Free all session variables

49. What are the different functions in sorting an array?

Sorting functions in PHP:

asort( )

arsort( )

ksort( )

krsort( )

uksort( )

sort( )

natsort( )

rsort( )

50. How can we know the count/number of elements of an array?

2 ways:

a) sizeof($array) - This function is an alias of count()

b) count($array) - This function returns the number of elements in an array.

Interestingly if you just pass a simple var instead of an array, count() will return 1.

51. What’s the difference between md5( ), crc32( ) and sha1( ) crypto on PHP?

The major difference is the length of the hash generated. CRC32 is, evidently, 32 bits, while sha1() returns a 160 bit value, and md5() returns a 128 bit value. This is important when avoiding collisions.

52. Will comparison of string "10" and integer 11 work in PHP?

Yes, internally PHP will cast everything to the integer type, so numbers 10 and 11 will be compared.

53. What are the differences between mysql_fetch_array(), mysql_fetch_object(), mysql_fetch_row() ?.

mysql_fetch_array() - Fetch a result row as a combination of associative array and

regular array.

mysql_fetch_object() - Fetch a result row as an object.

mysql_fetch_row() - Fetch a result set as a regular array().

The difference between mysql_fetch_row() and mysql_fetch_array() is that the first returns the results in a numeric array ($row[0], $row[1], etc.), while the latter returns a the results an array containing both numeric and associative keys ($row['name'], $row['email'], etc.). mysql_fetch_object() returns an object ($row->name, $row->email, etc.).

54. What is the difference between PHP4 and PHP5?

PHP4 cannot support oops concepts and Zend engine 1 is used.

PHP5 supports oops concepts and Zend engine 2 is used, Error supporting is increased in PHP5, XML and SQLLite will is increased in PHP5.

55. Can we use include(abc.PHP) two times in a PHP page makeit.PHP”?

Yes we can include that many times we want, but here are some things to make sure of:

(including abc.PHP, the file names are case-sensitive). There shouldn't be any duplicate function names, means there should not be functions or classes or variables with the same name in abc.PHP and makeit.php.

56. What is meant by nl2br()?

nl2br() inserts a HTML tag <br> before all new line characters \n in a string.

echo nl2br("god bless \n you");

output:

god bless<br>

you

57. How can I retrieve values from one database server and store them in other database server using PHP?

For this purpose, you can first read the data from one server into session variables. Then connect to other server and simply insert the data into the database.

58. In how many ways we can retrieve data in the result set of MYSQL using PHP?

mysql_fetch_array - Fetch a result row as an associative array, a numeric array, or both

mysql_fetch_assoc - Fetch a result row as an associative array

mysql_fetch_object - Fetch a result row as an object

mysql_fetch_row - Get a result row as an enumerated array

59. What are the functions for IMAP?

Internet message access protocol (IMAP) is one of the two most prevalent Internet standard protocols for e-mail retrieval, the other being the Post Office Protocol (POP).Virtually all modern e-mail clients and mail servers support both protocols as a means of transferring e-mail messages from a server. IMAP was designed by Mark Crispin in 1986. IMAP was previously known as Internet Mail Access Protocol, Interactive Mail Access Protocol (RFC 1064), and Interim Mail Access Protocol. The following are the some of IMAP functions commonly used.

imap_body - Read the message body

imap_check - Check current mailbox

imap_delete - Mark a message for deletion from current mailbox

imap_mail - Send an email message

imap_open - Open an IMAP stream to a mailbox

imap_close - Close an IMAP stream

imap_create - Alias of imap_createmailbox

imap_createmailbox - Create a new mailbox

imap_ping - Check if the IMAP stream is still active

60. How can we get the properties (size, type, width, height) of an image using php image functions?

getimagesize() - To know the image size

imagesx() - To know the image width

imagesy() - To know the image height

exif_imagetype - When a correct signature is found, the appropriate constant value

will be returned otherwise the return value is FALSE.

The return value is the same value that getimagesize()

returns in index 2 but exif_imagetype() is much faster.

The constant values mentioned above are IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG, IMAGETYPE_SWF, IMAGETYPE_PSD ,IMAGETYPE_BMP, IMAGETYPE_TIFF_II (intel byte order), IMAGETYPE_TIFF_MM (motorola byte order), IMAGETYPE_JPC,IMAGETYPE_JP2, IMAGETYPE_JPX, IMAGETYPE_JB2, IMAGETYPE_SWC, IMAGETYPE_IFF, IMAGETYPE_WBMP, IMAGETYPE_XBM, IMAGETYPE_ICO

61. How can we take a backup of a mysql table and how can we restore it?

Create a full backup of your database:

shell> mysqldump tab=/path/to/some/dir opt db_name

shell> mysqlhotcopy db_name /path/to/some/dir

The full backup file is just a set of SQL statements, so restoring it is very easy:

shell> mysql "."Executed";

Another way To backup:

BACKUP TABLE tbl_name TO /path/to/backup/directory

Another way To restore:

RESTORE TABLE tbl_name FROM /path/to/backup/directory

62. What is the maximum size of a file that can be uploaded using PHP and how can we change this?

Maximum upload size by default is 2MB. You can change maximum size of a file set upload_max_filesize variable in php.ini file

63. What’s the difference between accessing a class method via -> and via ::?

:: is allowed to access methods that can perform static operations, i.e. those, which do not require object initialization.

-> Is used to access the methods through objects

64. What type of inheritance that php supports?

In PHP an extended class is always dependent on a single base class, that is multiple inheritance is not supported. Classes are extended using the keyword 'extends'.

65. What changes I have to do in php.ini file for file uploading?

Make the following line uncomment like:

Whether to allow HTTP file uploads.

file_uploads = On

Temporary directory for HTTP uploaded files (will use system default if not specified).

upload_tmp_dir = C:\apache2triad\temp

Maximum allowed size for uploaded files.

upload_max_filesize = 2M

66. Steps for the payment gateway processing?

An online payment gateway is the interface between your merchant account and your Web site. The online payment gateway allows you to immediately verify credit card transactions and authorize funds on a customer's credit card directly from your Web site. It then passes the transaction off to your merchant bank for processing, commonly referred to as transaction batching.

67. What is the difference between Reply-to and Return-path in the headers of a mail function?

Reply-to :

Reply-to is where to delivery the reply of the mail.

Return-path :

Return path is when there is a mail delivery failure occurs then where to delivery the failure notification.

68. How to store the uploaded file to the final location?

move_uploaded_file ( string filename, string destination)

This function checks to ensure that the file designated by filename is a valid upload file (meaning that it was uploaded via PHP's HTTP POST upload mechanism). If the file is valid, it will be moved to the filename given by destination.

If filename is not a valid upload file, then no action will occur, and move_uploaded_file() will return FALSE.

If filename is a valid upload file, but cannot be moved for some reason, no action will occur, and move_uploaded_file() will return FALSE. Additionally, a warning will be issued.

69. Explain the ternary conditional operator in PHP?

Expression preceding the ? is evaluated, if it’s true, then the expression preceding the : is executed, otherwise, the expression following : is executed.

70. What’s the difference between include and require?

It’s how they handle failures. If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.

71. Explain about Type Juggling in php?

PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which that variable is used. That is to say, if you assign a string value to variable $var, $var becomes a string. If you then assign an integer value to $var, it becomes an integer.

An example of PHP's automatic type conversion is the addition operator '+'. If any of the operands is a float, then all operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer. Note that this does NOT change the types of the operands themselves; the only change is in how the operands are evaluated.

$foo += 2; // $foo is now an integer (2)

$foo = $foo + 1.3; // $foo is now a float (3.3)

$foo = 5 + "10 Little Piggies"; // $foo is integer (15)

$foo = 5 + "10 Small Pigs"; // $foo is integer (15)

If the last two examples above seem odd, see String conversion to numbers.

If you wish to change the type of a variable, see settype ( ).

If you would like to test any of the examples in this section, you can use the var_dump ( ) function.

Note: The behavior of an automatic conversion to array is currently undefined.

72. What does a special set of tags <?= and ?> do in PHP?

The output is displayed directly to the browser.

73. Would I use print "$a dollars" or "{$a} dollars" to print out the amount of dollars in this example?

In this example it wouldn’t matter, since the variable is all by itself, but if you were to print something like "{$a},000,000 mln dollars", then you definitely need to use the braces.

74. When are you supposed to use endif to end the conditional statement?

When the original if was followed by : and then the code block without braces.

75. Would you initialize your strings with single quotes or double quotes?

Since the data inside the single-quoted string is not parsed for variable substitution, it’s always a better idea speed-wise to initialize a string with single quotes, unless you specifically need variable substitution.

76. How come the code <?php print "Contents: $arr[1]"; ?> works, but

<?php print "Contents: $arr[1][2]"; ?> doesn’t for two-dimensional array of mine?.

Any time you have an array with more than one dimension, complex parsing syntax is required. print "Contents: {$arr[1][2]}" would’ve worked.

77. I want to combine two variables together: $var1 = 'Welcome to ';

$var2 = 'TechInterviews.com'; What will work faster? Code sample 1:$var 3 = $var1.$var2;

Or code sample 2:$var3 = "$var1$var2";

Both examples would provide the same result - $var3 equal to "Welcome to TechInterviews.com". However, Code Sample 1 will work significantly faster. Try it out with large sets of data (or via concatenating small sets a million times or so), and you will see that concatenation works significantly faster than variable substitution.

78. What is CAPTCHA?

CAPTCHA stands for Completely Automated Public Turing Test to tell Computers and Humans Apart. To prevent spammers from automatically fill out forms, CAPTCHA programmers will generate an image containing distorted images of a string of numbers and letters. Computers cannot determine what the numbers and letters are from the image but humans have great pattern recognition abilities and will be able to fairly accurately determine the string of numbers and letters. By entering the numbers and letters from the image in the validation field, the application can be fairly assured that there is a human client using it. To read more look here:

http://en.wikipedia.org/wiki/Captcha

79. If you have to work with dates in the following format: "Tuesday, February 14, 2006 @ 10:39 am", how can you convert them to another format, that is easier to use?

The strtotime function can convert a string to a timestamp. A timestamp can be converted to date format. So it is best to store the dates as timestamp in the database, and just output them in the format you like.

So let's say we have

$date = "Tuesday, February 14, 2006 @ 10:39 am";

In order to convert that to a timestamp, we need to get rid of the "@" sign, and we can use the remaining string as a parameter for the strtotime function.

So we have

$date = str_replace("@ ","",$date);

$date = strtotime($date);

now $date is a timestamp

and we can say:

echo date("d M Y",$date);

80. How i can get ip address?

We can use SERVER variable

$_SERVER['SERVER_ADDR'] and getenv("REMOTE_ADDR") functions to get the IP address.

81. What is differenc between mysql_connect and mysql_pconnect?

mysql_pconnect establishes a persistent connection. If you don't need one (such as a website that is mostly HTML files or PHP files that don't call the db) then you don't need to use it. mysql_connect establishes a connection for the duration of the script that access the db. Once the script has finished executing it closes the connection. The only time you need to close the connection manually is if you jump out of the script for any reason.

If you do use mysql_pconnect. You only need to call it once for the session. That's the beauty of it. It will hold open a connection to the db that you can use over and over again simply by calling the resource ID whenever you need to interact with the db.

82. What are the superglobal variables in php?.

There are number of superglobal variables in php

• $GLOBALS

• $_SERVER

• $_GET

• $_POST

• $_FILES

• $_COOKIE

• $_SESSION

• $_REQUEST

• $_ENV

83. What is the difference between Primary Key and Unique key?

Both Primary Key and Unique Key enforces uniqueness of the column on which they are defined. But by default Primary Key creates a Clustered Index on the column, where are Unique Key creates a Nonclustered Index by default. Another major difference is that, Primary Key doesn’t allow NULLs, but Unique Key allows one NULL only.

84. what are the most common caching policy approaches ?

1)Time triggered caching (expiry timestamp).

2)Content change triggered caching (sensitive content has changed, so cache must be updated).

3)Manually triggered caching (manually inform the application that information is outdated, and force a new cache creation).

85. How to prevent web browser to image caching ?.

The simple way to prevent image caching is to append time stamp with the name on image.

Example :

In the above code browser understand a new image at every call. But HTML parser understands“image.jpg” for every call.

86. How can we increase Memory size in php during run time?

using ini_set(‘memory_limit’,’15M’); // now 15M space is set during run time.

87. How to increase Execution Time Limit in php Using ini_set()

To increase the execution time for any php script simple use below code.

ini_set(‘max_execution_time’, 240); //240seconds = 4 minutes

88. Which of the variable that PHP makes automatically available to you ?

$_SERVER

89. Where the all webserver information is stored in PHP ?

$_SERVER is a PHP variable that contains all web server information It is known as a superglobal.

90. Differentiate between DROP a table and TRUNCATE a table?

DROP - It will delete the table and table data.

TRUNCATE - It will delete data of the table but not the table definition.

91. How will you change the name of a column in a table?

ALTER TABLE table_name CHANGE old_column_name new_column _name[new type]

92. How will you create a database using PHP and MySQL?

By using :

mysql_create_db("Database Name")

93. What is the purpose of the following files having extensions: frm, myd, and myi? What these files contain?

In MySQL, the default table type is MyISAM.

Each MyISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type.

The '.frm' file stores the table definition.

The data file has a '.MYD' (MYData) extension.

The index file has a '.MYI' (MYIndex) extension,

94. What is the maximum length of a table name, a database name, or a field name in MySQL?

Database name : 64 characters

Table name : 64 characters

Column name : 64 characters

95. How many values can the SET function of MySQL take?

MySQL SET function can take zero or more values, but at the maximum it can take 64 values.

96. What are the other commands to know the structure of a table using MySQL commands except EXPLAIN command?

DESCRIBE table_name;

97. How can we find the number of rows in a table using MySQL?

SELECT COUNT(*) FROM table_name;

98. How can we find the number of rows in a result set using PHP?

Here is how can you find the number of rows in a result set in PHP:

$result = mysql_query($any_valid_sql, $database_link);

$num_rows = mysql_num_rows($result);

echo "$num_rows rows found";

99. How many ways we can we find the current date using MySQL?

SELECT CURDATE();

SELECT CURRENT_DATE();

SELECT CURTIME();

SELECT CURRENT_TIME();

100. Give the syntax of GRANT commands?

The generic syntax for GRANT is as following

GRANT [rights] on [database] TO [username@hostname] IDENTIFIED BY [password]

Now rights can be:

a) ALL privilages

b) Combination of CREATE, DROP, SELECT, INSERT, UPDATE and DELETE etc.

We can grant rights on all databse by usingh *.* or some specific database by database.* or a specific table by database.table_name.

101. Give the syntax of REVOKE commands?

The generic syntax for revoke is as following

REVOKE [rights] on [database] FROM [username@hostname]

Now rights can be:

a) ALL privileges

b) Combination of CREATE, DROP, SELECT, INSERT, UPDATE and DELETE etc.

We can grant rights on all database by using *.* or some specific database by database.* or a specific table by database.table_name.

102. What is the difference between CHAR and VARCHAR data types?

CHAR is a fixed length data type. CHAR(n) will take n characters of storage even if you enter less than n characters to that column. For example, "Hello!" will be stored as "Hello! " in CHAR(10) column.

VARCHAR is a variable length data type. VARCHAR(n) will take only the required storage for the actual number of characters entered to that column. For example, "Hello!" will be stored as "Hello!" in VARCHAR(10) column.

103. How can we encrypt and decrypt a data present in a mysql table using mysql?

AES_ENCRYPT() and AES_DECRYPT()

AES_ENCRYPT(str, key_str)

AES_DECRYPT(crypt_str, key_str)

104. How can we know the number of days between two given dates using MySQL?

Use DATEDIFF()

SELECT DATEDIFF(NOW(),'2006-07-01');

105. What is the difference between GROUP BY and ORDER BY in SQL?

To sort a result, use an ORDER BY clause.

The most general way to satisfy a GROUP BY clause is to scan the whole table and create a new temporary table where all rows from each group are consecutive, and then use this temporary table to discover groups and apply aggregate functions (if any).

ORDER BY [col1],[col2],...[coln]; Tells DBMS according to what columns it should sort the result. If two rows will have the same value in col1 it will try to sort them according to col2 and so on.

GROUP BY [col1],[col2],...[coln]; Tells DBMS to group (aggregate) results with same value of column col1. You can use COUNT(col1), SUM(col1), AVG(col1) with it, if you want to count all items in group, sum all values or view average.

106. How can increase the performance of MySQL select query?

We can use LIMIT to stop MySql for further search in table after we have received our required no. of records, also we can use LEFT JOIN or RIGHT JOIN instead of full join in cases we have related data in two or more tables.

107. How can we change the name of a column of a table?

MySQL query to rename table:

RENAME TABLE tbl_name TO new_tbl_name

or,

ALTER TABLE tableName CHANGE OldName newName

108. How can we repair a MySQL table?

The syntex for repairing a mysql table is:

REPAIR TABLE tablename

REPAIR TABLE tablename QUICK

REPAIR TABLE tablename EXTENDED

This command will repair the table specified.

If QUICK is given, MySQL will do a repair of only the index tree.

If EXTENDED is given, it will create index row by row.

109. How can I load data from a text file into a table?

The MySQL provides a LOAD DATA INFILE command. You can load data from a file. Great tool but you need to make sure that:

a) Data must be delimited

b) Data fields must match table columns correctly

110. What is Joomla in PHP?

Joomla is a content management system. Powerful online applications and web sites are build using Joomla. Joomla is an open source CMS tool. Clients can easily manage their web sites with minimal amount of instructions. It is highly extensible. Joomla runs off PHP or MySQL. Joomla is used to create, maintain a structured, flexible portal, add or edit content, changes the look and feel of the site. PHP scripting is used and persisted most of its data / information in MySQL database.

111. What is meant by MIME?

MIME is Multipurpose Internet Mail Extensions is an Internet standard for the format of e-mail.

WWW's ability to recognize and handle files of different types is largely dependent on the use of the MIME (Multipurpose Internet Mail Extensions) standard. The standard provides for a system of registration of file types with information about the applications needed to process them. This information is incorporated into Web server and browser software, and enables the automatic recognition and display of registered file types.

However browsers also uses MIME standard to transmit files. MIME has a header which is added to a beginning of the data. When browser sees such header it shows the data as it would be a file (for example image)

Some examples of MIME types:

audio/x-ms-wmp

image/png

application/x-shockwave-flash

112. If we login more than one browser windows at the same time with same user and after that we close one window, then is the session is exist to other windows or not? And if yes then why? If no then why?

Session depends on browser. If browser is closed then session is lost. The session data will be deleted after session time out. If connection is lost and you recreate connection, then session will continue in the browser.

113. What are the difference between abstract class and interface?

Abstract class:

abstract classes are the class where one or more methods are abstract but not necessarily all method has to be abstract. Abstract methods are the methods, which are declare in its class but not define. The definition of those methods must be in its extending class.

Interface:

Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be define by its implemented class.

114. What are the advantages of stored procedures, triggers, indexes?

Stored procedures :

A stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don't need to keep re-issuing the entire query but can refer to the stored procedure. This provides better overall performance because the query has to be parsed only once, and less information needs to be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server. However, stored procedures of course do increase the load on the database server system, as more of the work is done on the server side and less on the client (application) side.

Triggers :

Triggers will also be implemented. A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that stored procedure automatically deletes the corresponding customer from a customer table when all his transactions are deleted.

Indexes :

Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine the position to seek to in the middle of the data file without having to look at all the data. If a table has 1,000 rows, this is at least 100 times faster than reading sequentially. If you need to access most of the rows, it is faster to read sequentially, because this minimizes disk seeks.

115. What are the different ways to login to a remote server? Explain the means, advantages and disadvantages?

Some of the ways to logon to a remote server are :

Use ssh

Use telnet if you concern with security

We can also use rlogin to logon to a remote server.

We can use Team viewer like applications

116. How can I set a cron and how can I execute it in Unix, Linux, and windows?

Cron is very simply a Linux module that allows you to run commands at predetermined times or intervals. In Windows, it's called Scheduled Tasks. The name Cron is in fact derived from the same word from which we get the word chronology, which means order of time.

The easiest way to use crontab is via the crontab command.

# crontab

This command 'edits' the crontab. Upon employing this command, you will be able to enter the commands that you wish to run. The syntax of this file is very important – if you get it wrong, your crontab will not function properly. The syntax of the file should be as follows:

minutes hours day_of_month month day_of_week command

All the variables, with the exception of the command itself, are numerical constants. In addition to an asterisk (*), which is a wildcard that allows any value, the ranges permitted for each field are as follows:

Minutes: 0-59

Hours: 0-23

Day_of_month: 1-31

Month: 1-12

Weekday: 0-6

We can also include multiple values for each entry, simply by separating each value with a comma.

command can be any shell command and, as we will see momentarily, can also be used to execute a Web document such as a PHP file.

So, if we want to run a script every Tuesday morning at 8:15 AM, our mycronjob file will contain the following content on a single line:

15 8 * * 2 /path/to/scriptname

This all seems simple enough, right? Not so fast! If you try to run a PHP script in this manner, nothing will happen (barring very special configurations that have PHP compiled as an executable, as opposed to an Apache module). The reason is that, in order for PHP to be parsed, it needs to be passed through Apache. In other words, the page needs to be called via a browser or other means of retrieving.

21 June 2012