PHP Interview questions 20

81) How we load all classes that placed in different directory in one PHP File , means how to do auto load classes

Ans :      by using spl_autoload_register('autoloader::funtion');

Like below

class autoloader

{

public static function moduleautoloader($class)

{

$path = $_SERVER['DOCUMENT_ROOT'] . "/modules/{$class}.php";

if (is_readable($path)) require $path;

}

public static function daoautoloader($class)

{

$path = $_SERVER['DOCUMENT_ROOT'] . "/dataobjects/{$class}.php";

if (is_readable($path)) require $path;

}

public static function includesautoloader($class)

{

$path = $_SERVER['DOCUMENT_ROOT'] . "/includes/{$class}.php";

if (is_readable($path)) require $path;

}

}

spl_autoload_register('autoloader::includesautoloader');

spl_autoload_register('autoloader::daoautoloader');

spl_autoload_register('autoloader::moduleautoloader');

82) How many types of Inheritances used in PHP and how we achieve it

Ans :      As far PHP concern it only support single Inheritance in scripting.

we can also use interface to achieve multiple inheritance.

                 

83)          PHP how to know user has read the email?

Ans :      Using Disposition-Notification-To: in mailheader we can get read receipt.

Add the possibility to define a read receipt when sending an email.

It’s quite straightforward, just edit email.php, and add this at vars definitions:

var $readReceipt = null;

And then, at ‘createHeader’ function add:

if (!empty($this->readReceipt)) {

$this->__header .= ‘Disposition-Notification-To: ‘ . $this->__formatAddress($this->readReceipt) . $this->_newLine;

}

84) What are default session time and path?

Ans :      default session time in PHP is 1440 seconds or 24 minutes

Default session save path id temporary folder /tmp

85) how to track user logged out or not? when user is idle ?

Ans : 85                By checking the session variable exist or not while loading th page. As the session will exist longer as till browser closes. The default behaviour for sessions is to keep a session open indefinitely and only to expire a session when the browser is closed. This behaviour can be changed in the php.ini file by altering the line session.cookie_lifetime = 0 to a value in seconds. If you wanted the session to finish in 5 minutes you would set this to session.cookie_lifetime = 300 and restart your httpd server.

PHP Interview questions 19

76) What is the difference between char and varchar data types?

Ans :      Set char to occupy n bytes and it will take n bytes even if u r storing a value of n-m bytes

Set varchar to occupy n bytes and it will take only the required space and will not use the n bytes

eg. name char(15) will waste 10 bytes if we store 'romharshan', if each char takes a byte eg. name varchar(15) will just use 5 bytes if we store 'romharshan', if each char takes a byte. rest 10 bytes will be free.

77) What is the functionality of md5 function in PHP?

Ans :      Calculate the md5 hash of a string. The hash is a 32-character hexadecimal number. I use it to generate keys which I use to identify users etc. If I add random no techniques to it the md5 generated now will be totally different for the same string I am using.

78) How can I load data from a text file into a table?

Ans :      you can use LOAD DATA INFILE file_name; syntax to load data from a text file. but you have to make sure thata) data is delimited

b) columns and data matched correctly

79) How can we know the number of days between two given dates using MySQL?

Ans :      SELECT DATEDIFF("2007-03-07","2005-01-01");

                 

80) How can we know the number of days between two given dates using PHP?

Ans :      $date1 = date("Y-m-d");

$date2 = "2006-08-15";

$days = (strtotime($date1) - strtotime($date2)) / (60 * 60 * 24);

PHP Interview questions 18

71) What type of inheritance that PHP supports?

Ans :      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'.

72) What is the difference between Primary Key and Unique key?

Ans :      Primary Key: A column in a table whose values uniquely identify the rows in the table. A primary key value cannot be NULL.

Unique Key: Unique Keys are used to uniquely identify each row in the table. There can be one and only one row for each unique key value. So NULL can be a unique key.There can be only one primary key for a table but there can be more than one unique for a table.

                 

73) what is garbage collection? default time ? refresh time?

Ans : Garbage Collection is an automated part of PHP , If the Garbage Collection process runs, it then analyzes any files in the /tmp for any session files that have not been accessed in a certain amount of time and physically deletes them. Garbage Collection process only runs in the default session save directory, which is /tmp. If you opt to save your sessions in a different directory, the Garbage Collection process will ignore it. the Garbage Collection process does not differentiate between which sessions belong to whom when run. This is especially important note on shared web servers. If the process is run, it deletes ALL files that have not been accessed in the directory. There are 3 PHP.ini variables, which deal with the garbage collector: PHP ini value name default session.gc_maxlifetime 1440 seconds or 24 minutes session.gc_probability 1 session.gc_divisor 100

74) What are the advantages/disadvantages of MySQL and PHP?

Ans :      Both of them are open source software (so free of cost), support cross platform. php is faster then ASP and JSP.

75) What is the difference between GROUP BY and ORDER BY in Sql?

Ans :      ORDER BY [col1],[col2],…,[coln]; Tels DBMS according to what columns it should sort the result. If two rows will hawe the same value in col1 it will try to sort them according to col2 and so on.GROUP BY [col1],[col2],…,[coln]; Tels DBMS to group 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  

PHP Interview questions 17

66) Explain Normalization concept?

Ans : The normalization process involves getting our data to conform to three progressive normal forms, and a higher level of normalization cannot be achieved until the previous levels have been achieved (there are actually five normal forms, but the last two are mainly academic and will not be discussed).First Normal FormThe First Normal Form (or 1NF) involves removal of redundant data

from horizontal rows. We want to ensure that there is no duplication of data in a given row, and that every column stores the least amount of information possible (making the field atomic).Second Normal FormWhere the First Normal Form deals with redundancy of data across a horizontal row, Second Normal Form (or 2NF) deals with redundancy of data in vertical columns. As stated earlier, the normal forms are progressive, so to achieve Second Normal Form, your tables must already be in First Normal Form.Third Normal Form I have a confession to make; I do not often use Third Normal Form. In Third Normal Form we are looking for data in our tables that is not fully dependant on the primary key, but dependant on another value in the table            

67) How can we find the number of rows in a table using MySQL?

Ans :      Use this for mysql

>SELECT COUNT(*) FROM table_name;

68) How can we find the number of rows in a result set using PHP?

Ans :      $result = mysql_query($sql, $db_link);

$num_rows = mysql_num_rows($result);

echo "$num_rows rows found";

69) How many ways we can we find the current date using MySQL?

Ans : 69                SELECT CURDATE();

CURRENT_DATE() = CURDATE()

for time use

SELECT CURTIME();

CURRENT_TIME() = CURTIME()

70) What are the advantages and disadvantages of Cascading Style Sheets?

Ans : External Style SheetsAdvantagesCan control styles for multiple documents at once. Classes can be

created for use on multiple HTML element types in many documents. Selector and grouping methods can be used to apply styles under complex contextsDisadvantagesAn extra download is required to import style information for each document The rendering of the document may be delayed until the external style sheet is loaded Becomes slightly unwieldy for small quantities of style definitionsEmbedded Style Sheets Advantages Classes can be created for use on multiple tag types in the document.

Selector and grouping methods can be used to apply styles under complex contexts. No additional downloads necessary to receive style information

Disadvantages

This method can not control styles for multiple documents at once Inline Styles

Advantages

Useful for small quantities of style definitions. Can override other style specification methods at the local level so only exceptions need to be listed in conjunction with other style methods

Disadvantages

Does not distance style information from content (a main goal of SGML/HTML). Can not control styles for multiple documents at once.

Author can not create or control classes of elements to control multiple element types within the document. Selector grouping methods can not be used to create complex element addressing scenarios

PHP Interview questions 16

61) What are the other commands to know the structure of table using MySQL commands except explain command?

Ans :      describe Table-Name;

                 

62) How many tables will create when we create table, what are they?

Ans :      The '.frm' file stores the table definition.

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

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

                 

 63) What is the purpose of the following files having extensions 1) .frm 2) .myd 3) .myi? What do these files contain?

Ans :      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,

64) What is maximum size of a database in MySQL?

Ans :      If the operating system or filesystem places a limit on the number of files in a directory, MySQL is bound by that constraint.The efficiency of the operating system in handling large numbers of files in a directory can place a practical limit on the number of tables in a database. If the time required to open a file in the directory increases significantly as the number of files increases, database performance can be adversely affected.

The amount of available disk space limits the number of tables.

MySQL 3.22 had a 4GB (4 gigabyte) limit on table size. With the MyISAM storage engine in MySQL 3.23, the maximum table size was increased to 65536 terabytes (2567 – 1 bytes). With this larger allowed table size, the maximum effective table size for MySQL databases is usually determined by operating system constraints on file sizes, not by MySQL internal limits.The InnoDB storage engine maintains InnoDB tables within a tablespace that can be created from several files. This allows a table to exceed

the maximum individual file size. The tablespace can include raw disk partitions, which allows extremely large tables. The maximum tablespace size is 64TB.

The following table lists some examples of operating system file-size limits. This is only a rough guide and is not intended to be definitive. For the most up-to-date information, be sure to check the documentation specific to your operating system.

Operating System File-size LimitLinux 2.2-Intel 32-bit 2GB (LFS: 4GB)

Linux 2.4+ (using ext3 filesystem) 4TB

Solaris 9/10 16TB

NetWare w/NSS filesystem 8TB

Win32 w/ FAT/FAT32 2GB/4GB

Win32 w/ NTFS 2TB (possibly larger)

MacOS X w/ HFS+ 2TB

65) Give the syntax of Grant and Revoke commands?

Ans :      The generic syntax for grant is as following

> GRANT [rights] on [database/s] TO [username@hostname] IDENTIFIED BY [password] now rights can be

a) All privileges

b) combination of create, drop, select, insert, update and delete etc.We can grant rights on all databse by using *.* or some specific database by database.* or a specific table by database.table_name

username@hotsname can be either username@localhost, username@hostname and username@%

where hostname is any valid hostname and % represents any name, the *.* any condition password is simply the password of userThe generic syntax for revoke is as following > REVOKE [rights] on  [database/s] FROM [username@hostname] now rights can be as explained above

a) All privileges

b) combination of create, drop, select, insert, update and delete etc.

username@hotsname can be either username@localhost, username@hostname and username@%

where hostname is any valid hostname and % represents any name, the *.*

any condition

PHP Interview question 15

56) How can we send mail using JavaScript?

Ans :      JavaScript does not have any networking capabilities as it is designed to work on client site. As a result we can not send mails using JavaScript. But we can call the client side mail protocol mailto

via JavaScript to prompt for an email to send. this requires the client to approve it.

57 How can we repair a MySQL table?

Ans :      The syntex for repairing a MySQL table is

REPAIR TABLENAME, [TABLENAME, ], [Quick],[Extended]

This command will repair the table specified if the quick is given the MySQL will do a repair of only the index tree if the extended is given it will create index row by row               

58) What are the advantages of stored procedures, triggers, indexes?

Ans :      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 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 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.                

59) What is the maximum length of a table name, database name, and fieldname in MySQL?

Ans :      The following table describes the maximum length for each type of identifier.

Identifier             Maximum Length (bytes)

Database             64

Table     64

Column                64

Index    64

Alias       255

There are some restrictions on the characters that may appear in identifiers:

60) How many values can the SET function of MySQL take?

Ans :      MySQL set can take zero or more values but at the maximum it can take 64 values           

PHP Interview question 14

51) List out some tools through which we can draw E-R diagrams for mysql.

Ans :      Case Studio

Smart Draw

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

Ans :      we can always fetch from one database and rewrite to another. Here is a nice solution of it.$db1 = mysql_connect("host","user","pwd")

mysql_select_db("db1", $db1);

$res1 = mysql_query("query",$db1);$db2 = mysql_connect("host","user","pwd")

mysql_select_db("db2", $db2);

$res2 = mysql_query("query",$db2);At this point you can only fetch records from you previous ResultSet,

i.e $res1 But you cannot execute new query in $db1, even if you supply the link as because the link was overwritten by the new db.so at this point the following script will fail

$res3 = mysql_query("query",$db1); //this will failSo how to solve that?

take a look below.

$db1 = mysql_connect("host","user","pwd")

mysql_select_db("db1", $db1);

$res1 = mysql_query("query",$db1);

$db2 = mysql_connect("host","user","pwd", true)

mysql_select_db("db2", $db2);

$res2 = mysql_query("query",$db2);

So mysql_connect has another optional boolean parameter which indicates whether a link will be created or not. as we connect to the $db2 with this optional parameter set to 'true', so both link will

remain live.

now the following query will execute successfully.

$res3 = mysql_query("query",$db1);

53)  List out the predefined classes in PHP?

Ans :      Directory

stdClass

__PHP_Incomplete_Class

exception

php_user_filter

                 

54) How can I make a script that can be bi-language (supports English, German)?

Ans :      You can maintain two separate language file for each of the language. all the labels are putted in both language files as variables and assign those variables in the PHP source. on runtime choose the

required language option.

55) What are the difference between abstract class and interface?

Ans :      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.

PHP Interview question 13

46) What is the difference between ereg_replace() and eregi_replace()?

Ans : eregi_replace() function is identical to ereg_replace() except that this ignores case distinction when matching alphabetic characters.eregi_replace() function is identical to ereg_replace() except that this ignores case distinction when matching alphabetic characters.

47) What are the different functions in sorting an array?

Ans :      Sort(), arsort(), asort(), ksort(), natsort(), natcasesort(), rsort(), usort(), array_multisort(), and

uksort().

48) How can we know the count/number of elements of an array?

Ans :      2 ways

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

b) count($urarray)

49) what is session_set_save_handler in PHP?

Ans :      session_set_save_handler() sets the user-level session storage functions which are used for storing and retrieving data associated with a session. This is most useful when a storage method other than those supplied by PHP sessions is preferred. i.e. Storing the session data in a local database.          

50) How can I know that a variable is a number or not using a JavaScript?

Ans :      bool is_numeric ( mixed var)

Returns TRUE if var is a number or a numeric string, FALSE otherwise.or use isNaN(mixed var)The isNaN() function is used to check if a value is not a number.

PHP Interview question 12

41) How can we optimize or increase the speed of a MySQL select query?

Ans:  first of all instead of using select * from table1, use select  column1, column2, column3.. from table1 Look for the opportunity to introduce index in the table you are querying. use limit keyword if you are looking for any specific number of rows from the result set.

42) How many ways can we get the value of current session id?

Ans :      session_id() returns the session id for the current session.

43) How can we destroy the session, how can we unset the variable of a session?

Ans :  session_unregister  Unregister a global variable from the current Session session_unset Free all session variables

44) How can we set and destroy the cookie n php?

Ans :      By using setcookie(name, value, expire, path, domain); function we can set the cookie in php ;

Set the cookies in past for destroy. Like setcookie("user", "sonia", time()+3600); for set the cookie

setcookie("user", "", time()-3600); for destroy or delete the cookies;      

45) How many ways we can pass the variable through the navigation between the pages?

Ans : GET/QueryString

    POST                 

PHP Interview question 11

36) How can we get the properties (size, type, width, height) of an image using PHP image functions?

Ans:       To know the Image type use exif_imagetype () function

To know the Image size use getimagesize () function

To know the image width use imagesx () function

To know the image height use imagesy() function t

37) How can we get the browser properties using PHP?

Ans :      By using

$_SERVER['HTTP_USER_AGENT'] variable.

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

Ans :      By default the maximum size is 2MB. and we can change the following setup at php.iniupload_max_filesize = 2M

39) How can we increase the execution time of a PHP script?

Ans :      by changing the following setup at php.ini max_execution_time = 30; Maximum execution time of each script, in seconds                

40) How can we take a backup of a MySQL table and how can we restore it. ?

Ans :      To backup: BACKUP TABLE tbl_name[,tbl_name¦] TO '/path/to/backup/directory' RESTORE TABLE tbl_name[,tbl_name¦] FROM '/path/to/backup/directory'mysqldump: Dumping Table Structure and DataUtility to dump a database or a collection of database for backup or for transferring the data to another SQL server (not necessarily a MySQL server). The dump will contain SQL statements to create the table and/or populate the table.

-t, no-create-info

Don't write table creation information (the CREATE TABLE statement).

-d, no-data

Don't write any row information for the table. This is very useful if you just want to get a dump of the structure for a table!

PHP Interview question 10

31) How can we get second of the current time using date function?

Ans :      $second = date("s");      

 

32) How can we convert the time zones using PHP?

Ans :      By using date_default_timezone_get and date_default_timezone_set function on PHP 5.1.0

<?php

// Discover what 8am in Tokyo relates to on the East Coast of the US   

// Set the default timezone to Tokyo time:

date_default_timezone_set('Asia/Tokyo');   

// Now generate the timestamp for that particular timezone, on Jan 1st, 2000

$stamp = mktime(8, 0, 0, 1, 1, 2000);   

// Now set the timezone back to US/Eastern

date_default_timezone_set('US/Eastern');   

// Output the date in a standard format (RFC1123), this will print:

// Fri, 31 Dec 1999 18:00:00 EST

echo '<p>', date(DATE_RFC1123, $stamp) ,'</p>';?>

33) What is meant by urlencode and urldocode?

Ans :      URLencode returns a string in which all non-alphanumeric characters except -_. have been replaced with a percent (%) sign followed by two hex digits and spaces encoded as plus (+) signs. It is encoded the same way that the posted data from a WWW form is encoded, that is the same way as in application/x-www-form-urlencoded media type.

urldecode decodes any %## encoding in the given string.

34) What is the difference between the functions unlink and unset?

Ans :      unlink() deletes the given file from the file system.

unset() makes a variable undefined.

35) How can we register the variables into a session?

Ans :      $_SESSION['name'] = "sonia";

PHP Interview question 9

26) What are the different types of errors in PHP?

Ans :      Three are three types of errors:

1. 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, as you will see, you can change this default behavior.

2. 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.3.

3.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.

27) What is the functionality of the function strstr and stristr?

Ans :      strstr Returns part of string from the first occurrence of needle(sub string that we finding out ) to the end of string.

$email= 'sonialouder@gmail.com';

$domain = strstr($email, '@');

echo $domain; // prints @gmail.com

here @ is the needle

stristr is case-insensitive means able not able to diffrenciate between a and A

28) What are the differences between PHP 3 and PHP 4 and PHP 5?

Ans : There are lot of difference among these three version of php

1>Php3 is oldest version after that php4 came and current version is php5 (php5.3) where php6 have to come

2>Difference mean oldest version have less functionality as compare to new one like php5 have all OOPs concept now where as php3 was pure procedural language constructive like C

In PHP5 1. Implementation of exceptions and exception handling

2. Type hinting which allows you to force the type of a specific argument

3. Overloading of methods through the __call function

4. Full constructors and destructors etc through a __constuctor and __destructor function

5. __autoload function for dynamically including certain include files depending on the class you are trying to create.

6 Finality : can now use the final keyword to indicate that a method cannot be overridden by a child. You can also declare an entire class as final which prevents it from having any children at all.

7 Interfaces & Abstract Classes

8 Passed by Reference :

9 An __clone method if you really want to duplicate an object

10 Numbers of Functions Deprecated in php 5.x like ereg,ereg_replace,magic_quotes_runtime, session_register,register_globals, split(), call_user_method() etc

                 

29) How can we convert asp pages to PHP pages?

Ans :      there are lots of tools available for asp to PHP conversion. you can search Google for that. the best one is available at http://asp2php.naken.cc./

30) What is the functionality of the function htmlentities?

Ans :      Convert all applicable characters to HTML entities

This function is identical to htmlspecialchars() in all ways, except with htmlentities(), all characters which have HTML character entity equivalents are translated into these entities.