PHP-MYSQL Interview Questions and Answers

1. How many ways can we get the value of current session id?

Session_id() returns the session id for the current session.

2. What is the difference between mysql_fetch_object and mysql_fetch_array?

MySQL fetch object will collect first single matching record where mysql_fetch_array will collect all matching records from the table in an array.

3. What is meant by urlencode and urldecode?

Answer 1:
urlencode() returns the URL encoded version of the given string. URL coding converts special characters into % signs followed by two hex digits. For example: urlencode(“10.00%”) will return “10%2E00%25”. URL encoded strings are safe to be used as part of URLs.
urldecode() returns the URL decoded version of the given string.

Answer 2:
string urlencode(str) – Returns the URL encoded version of the input string. String values to be used in URL query string need to be URL encoded. In the URL encoded version:

Alphanumeric characters are maintained as is.
Space characters are converted to “+” characters.
Other non-alphanumeric characters are converted “%” followed by two hex digits representing the converted character.

string urldecode(str) – Returns the original string of the input URL encoded string.

For example:

$discount =”10.00%”;
$url = “http://domain.com/submit.php?disc=”.urlencode($discount);
echo $url;

You will get “http://domain.com/submit.php?disc=10%2E00%25”.

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

Answer 1:
$message is a simple variable whereas $$message is a reference variable. Example:
$user = ‘bob’

is equivalent to

$holder = ‘user’;
$$holder = ‘bob’;

Answer 2:
They are both variables. But $message is a variable with a fixed name. $$message is a variable who’s name is stored in $message. For example, if $message contains “var”, $$message is the same as $var.

5. What does a special set of tags do in PHP?

What does a special set of tags do in PHP?
The output is displayed directly to the browser.

6. What Is a Persistent Cookie?

A persistent cookie is a cookie which is stored in a cookie file permanently on the browser’s 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

7. How can we encrypt the username and password using PHP?

Answer1
You can encrypt a password with the following Mysql>SET PASSWORD=PASSWORD(“Password”);

Answer2
You can use the MySQL PASSWORD() function to encrypt username and password. For example,
INSERT into user (password, …) VALUES (PASSWORD($password”)), …);

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

Func_num_args() function returns the number of parameters passed in

9. How do you define a constant?

Via define() directive, like define (“MYCONSTANT”, 100);

10. What are the differences between require and include, include_once?

Answer 1:
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.

Answer 2:
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. The major difference between include() and require() is that in failure include() produces a warning message whereas require() produces a fatal errors.

Answer 3:
All three are used to an include file into the current page.
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.

Answer 4:
File will not be included more than once. If we want to include a file once only and further calling of the file will be ignored then we have to use the PHP function include_once(). This will prevent problems with function redefinitions, variable value reassignments, etc.

11. How To Get the Uploaded File Information in the Receiving Script?

Once the Web server received the uploaded file, it will call the PHP script specified in the form action attribute to process them. This receiving PHP script can get the uploaded file information through the predefined array called $_FILES. Uploaded file information is organized in $_FILES as a two-dimensional array as:
$_FILES[$fieldName][‘name’] – The Original file name on the browser system.
$_FILES[$fieldName][‘type’] – The file type determined by the browser.
$_FILES[$fieldName][‘size’] – The Number of bytes of the file content.
$_FILES[$fieldName][‘tmp_name’] – The temporary filename of the file in which the uploaded file was stored on the server.
$_FILES[$fieldName][‘error’] – The error code associated with this file upload.

The $fieldName is the name used in the <INPUT,>.

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

Just run the PHP CLI (Command Line Interface) program and provide the PHP script file name as the command line argument. For example, “php myScript.php”, assuming “php” is the command to invoke the CLI program.
Be aware that if your PHP script was written for the Web CGI interface, it may not execute properly in command line environment.

13. I am trying to assign a variable the value of 0123, but it keeps coming up with a different number, what’s the problem?

PHP Interpreter treats numbers beginning with 0 as octal. Look at the similar PHP interview questions for more numeric problems.

14. 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.

15. What are the different tables present in MySQL? Which type of table is generated when we are creating a table in the following syntax: create table employee(eno int(2),ename varchar(10))?

Total 5 types of tables we can create

1. MyISAM
2. Heap
3. Merge
4. INNO DB
5. ISAM MyISAM is the default storage engine as of MySQL 3.23. When you fire the above create query MySQL will create a MyISAM table.

16. How To Create a Table?

If you want to create a table, you can run the CREATE TABLE statement as shown in the following sample script:

<?php
include “mysql_connection.php”;

$sql = “CREATE TABLE Tech_links (”
. ” id INTEGER NOT NULL”
. “, url VARCHAR(80) NOT NULL”
. “, notes VARCHAR(1024)”
. “, counts INTEGER”
. “, time TIMESTAMP DEFAULT sysdate()”
. “)”;
if (mysql_query($sql, $con)) {
print(“Table Tech_links created.\n”);
} else {
print(“Table creation failed.\n”);
}

mysql_close($con);
?>

Remember that mysql_query() returns TRUE/FALSE on CREATE statements. If you run this script, you will get something like this:
Table Tech_links created.

17. How can we encrypt the username and password using PHP?

Answer1
You can encrypt a password with the following Mysql>SET PASSWORD=PASSWORD(“Password”);

Answer2
You can use the MySQL PASSWORD() function to encrypt username and password. For example,
INSERT into user (password, …) VALUES (PASSWORD($password”)), …);

18. How do you pass a variable by value?

Just like in C++, put an ampersand in front of it, like $a = &$b

19. 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.

20. 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.

21. How can we send mail using JavaScript?

No. There is no way to send emails directly using JavaScript.

But you can use JavaScript to execute a client side email program send the email using the “mailto” code. Here is an example:

function myfunction(form)
{
tdata=document.myform.tbox1.value;
location=”mailto:mailid@domain.com?subject=…”;
return true;
}

22. What is the difference between ereg_replace() and eregi_replace()?

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

23. 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,

24. If the variable $a is equal to 5 and variable $b is equal to character a, what’s the value of $$b?

100, it’s a reference to existing variable.

25. How To Protect Special Characters in Query String?

If you want to include special characters like spaces in the query string, you need to protect them by applying the urlencode() translation function. The script below shows how to use urlencode():

<?php
print(“<html>”);
print(“<p>Please click the links below”
.” to submit comments about TECHPreparation.com:</p>”);
$comment = ‘I want to say: “It\’s a good site! :->”‘;
$comment = urlencode($comment);
print(“<p>”
.”<a href=\”processing_forms.php?name=Guest&comment=$comment\”>”
.”It’s an excellent site!</a></p>”);
$comment = ‘This visitor said: “It\’s an average site! :-(“‘;
$comment = urlencode($comment);
print(“<p>”
.'<a href=”processing_forms.php?’.$comment.’”>’
.”It’s an average site.</a></p>”);
print(“</html>”);
?>

26. Are objects passed by value or by reference?

Everything is passed by value.

27. What are the differences between DROP a table and TRUNCATE a table?

DROP TABLE table_name – This will delete the table and its data.

TRUNCATE TABLE table_name – This will delete the data of the table, but not the table definition.

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

parent::constructor($value)

29. WHAT ARE THE DIFFERENT TYPES OF ERRORS IN PHP?

Here are three basic types of runtime errors in PHP:

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 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. 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

30. 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.

31. How can we submit a form without a submit button?

If you don’t want to use the Submit button to submit a form, you can use normal hyper links to submit a form. But you need to use some JavaScript code in the URL of the link. For example:

<a href=”javascript: document.myform.submit();”>Submit Me</a>