PHP-MySQL Interview Question

Q:1 What are the differences between Get and post methods in form submitting.
give the case where we can use get and we can use post methods?

A:1
–>If the processing of a form is idempotent (i.e. it has no lasting observable effect on the state of the world), then the form method should be GET. Many database searches have no visible side-effects and make ideal applications of query forms.
–
–>If the service associated with the processing of a form has side effects (for example, modification of a database or subscription to a service), the method should be POST.

How the form data is transmitted?

I would prefer POST when I don’t want the status to be change when user resubmits. And GET when it does not matter.

Q:2 Who is the father of PHP and explain the changes in PHP versions?

A:2 Rasmus Lerdorf is known as the father of PHP.PHP/FI 2.0 is an early and no longer supported version of PHP. PHP 3 is the successor to PHP/FI 2.0 and is a lot nicer. PHP 4 is the current generation of PHP, which uses the Zend engine under the hood. PHP 5 uses Zend engine 2 which, among other things, offers many additionalOOP features.

Q:3 How can we submit a form without a submit button?

A:3 The main idea behind this is to use Java script submit() function in order to submit the form without explicitly clicking any submit button You can attach the document.formname.submit() method to onclick, onchange events of different inputs and perform the form submission. you can even built a timer function where you can automatically submit the form after xx seconds once the loading is done (can be seen in online test sites).

Q:4 In how many ways we can retrieve the data in the result set of MySQL using PHP?

A:4 You can do it by 4 Ways
1. mysqlfetchrow.
2. mysqlfetcharray
3. mysqlfetchobject
4. mysqlfetchassoc

Q:5 What is the difference between mysqlfetchobject and mysqlfetcharray?

A:5 mysqlfetchobject() is similar tomysqlfetcharray(), with one difference - an object is returned, instead of an array. Indirectly, that means that you can only access the data by the field names, and not by their
offsets (numbers are illegal property names).

Q:6 What is the difference between $message and $$message?

A:6 It is a classic example of PHP’s variable variables. take the following example.$message = “Mizan”;$$message = “is a moderator of PHPXperts.”;$message is a simple PHP variable that we are used to. But the $$message is not a very familiar face. It creates a variable name $mizan with the value “is a moderator of PHPXperts.” assigned. break it like this${$message} => $mizanSometimes it is convenient to be able to have variable variable names. That is, a variable name which can be set and used dynamically.

Q:7 How can we extract string ‘abc.com ‘ from a string ‘http://info@abc.com’
using regular expression of PHP?

A:7 pregmatch(“/^http://.+@(.+)$/”,’http://info@abc.com’,$found);
echo $found[1];

Q:8 How can we create a database using PHP and MySQL?

A:8 We can create MySQL database with the use of
mysqlcreatedb(“Database Name”)

Q:9 What are the differences between require and include, includeonce and requireonce?

A:9 The include() statement includes and evaluates the specified file.The documentation below also applies to require().

The two constructs are identical in every way except how they handle failure. include() produces a Warning while require() results in a Fatal Error. In other words, use require() if you want a missing file to halt processing of the page.
include() does not behave this way, the script will continue regardless.

The includeonce() 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. As the name suggests, it will be included just once.includeonce() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc.

requireonce() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc.

Q:10 Can we use include (”abc.PHP”) two times in a PHP page “makeit.PHP”?

A:10 Yes we can use include() more than one time in any page though it is not a very good practice.

Q:11 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)) ?

A:11 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 and as a result if we do not specify the table name explicitly it will be assigned to the default engine.

Q:12 Functions in IMAP, POP3 AND LDAP?

A:12 You can find these specific information in PHP Manual.

Q:13 How can I execute a PHP script using command line?

A:13 As of version 4.3.0, PHP supports a new SAPI type (Server Application Programming Interface) named CLI which means Command Line Interface. 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.

Q:14 Suppose your Zend engine supports the mode Then how can u configure your PHP Zend engine to support mode ?

A:14 In php.ini file:
set
shortopentag=on
to make PHP support

Q:15 Shopping cart online validation i.e. how can we configure Paypal, etc.?

Q:15 Shopping cart online validation i.e. how can we configure Paypal, etc.?
A:15 We can find the detail documentation about different paypal integration process at the following site
PayPal PHP
SDK : http://www.paypaldev.org

Q:16 What is meant by nl2br()?

A:16 Inserts HTML line breaks before all newlines in a string string nl2br (string); Returns string with ” inserted before all newlines. For example: echo nl2br(“god blessn you”) will output “god bless you” to your browser.

Q:17 Draw the architecture of Zend engine?

A:17 The Zend Engine is the internal compiler and runtime engine used by PHP4. Developed by Zeev Suraski and Andi Gutmans, the Zend Engine is an abbreviation of their names. In the early days of PHP4, it worked as follows:

The PHP script was loaded by the Zend Engine and compiled into Zend opcode. Opcodes, short for operation codes, are low level binary instructions. Then the opcode was executed and the HTML generated sent to the client. The opcode was flushed from memory after execution.Today, there are a multitude of products and techniques to help you speed up this process. In the following diagram, we show the how modern PHP scripts work; all the shaded boxes are optional. PHP Scripts are loaded into memory and compiled into Zend opcodes.

Q:18 What are the current versions of apache, PHP, and MySQL?

A:18 As of February, 2007 the current versions arePHP: php5.2.1 MySQL: MySQL 5.2 Apache: Apache 2.2.4Note: visit www.php.net,
http://dev.mysql.com/downloads/mysql/,
www.apache.org to get current versions.

Q:19 What are the reasons for selecting lamp (Linux, apache, MySQL,PHP) instead of combination of other software programs, servers and operating systems?

A:19 All of those are open source resource. Security of Linux is very 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.

Q:20 How can we encrypt and decrypt a data present in a MySQL table using MySQL?

A:20 AESENCRYPT () and AESDECRYPT ()

Q:21 How can we encrypt the username and password using PHP?
A:21 The functions in this section perform encryption and decryption, and
compression and uncompression:

encryption decryption
AESENCRYT() AESDECRYPT()
ENCODE() DECODE()
DESENCRYPT() DESDECRYPT()
ENCRYPT() Not available
MD5() Not available
OLDPASSWORD() Not available
PASSWORD() Not available
SHA() or SHA1() Not available
Not available UNCOMPRESSEDLENGTH()

Q:22 What are the features and advantages of object-oriented
programming?
A:22 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

Q:23 What are the differences between procedure-oriented languages and
object-oriented languages?
A:23 Traditional programming has the following characteristics:Functions are written sequentially, so that a change in programming can affect any code that follows it. If a function is used multiple times in a system (i.e., a piece of code
that manages the date), it is often simply cut and pasted into each program (i.e., a change log, order function, fulfillment system, etc). If a date change is needed (i.e., Y2K when the code needed to be changed to handle four numerical digits instead of two), all these pieces of code must be found, modified, and tested. Code (sequences of computer instructions) and data (information on which the instructions operates on) are kept separate. Multiple sets of code can access and modify one set of data. One set of code may rely on data in multiple places. Multiple sets of code and data are required to work together. Changes made to any of the code sets and data sets can cause problems through out the system.Object-Oriented programming takes a radically different approach:Code and data are merged into one indivisible item – an object (the term “component” has also been used to describe an object.) An object is an abstraction of a set of real-world things (for example, an object may be created around “date”) The object would contain all information and functionality for that thing (A date object it may contain labels like January, February, Tuesday, Wednesday.
It may contain functionality that manages leap years, determines if it is a business day or a holiday, etc., See Fig. 1). Ideally, information about a particular thing should reside in only one place in a system. The information within an object is encapsulated (or hidden) from the rest of the system.
A system is composed of multiple objects (i.e., date function, reports, order processing, etc., See Fig 2). When one object needs information from another object, a request is sent asking for specific information. (for example, a report object may need to know what today’s date is and will send a request to the date object) These requests are called messages and each object has an interface that manages messages. OO programming languages include features such as “class”, “instance”, “inheritance”, and “polymorphism” that increase the power and flexibility of an object.

Q:24 What is the use of friend function?
A:24 Sometimes a function is best shared among a number of different classes. Such functions can be declared either as member functions of one class or as global functions. In either case they can be set to be friends of other classes, by using a friend specifier in the class that is admitting them. Such functions can use all attributes of the class which names them as a friend, as if they were themselves members of that class.

A friend declaration is essentially a prototype for a member function, but instead of requiring an implementation with the name of that class attached by the double colon syntax, a global function or member function of another class provides the match.

Q:25 What are the differences between public, private, protected,
static, transient, final and volatile?
A:25 Public: Public declared items can be accessed everywhere.
Protected: Protected limits access to inherited and parent classes (and to the class that defines the item).
Private: Private limits visibility only to the class that defines the item.
Static: A static variable exists only in a local function scope, but it does not lose its value when program execution leaves this scope.
Final: Final keyword prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.
transient: A transient variable is a variable that may not be serialized.
volatile: a variable that might be concurrently modified by multiple threads should be declared volatile. Variables declared to be volatile will not be optimized by the compiler because their value can change at any time.

Q:26 What are the different types of errors in PHP?
A:26 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. 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.

Q:27 What is the functionality of the function strstr and stristr?
A:27 strstr:

Returns part of haystack string from the first occurrence of needle to the end of haystack.If needle is not found, returns FALSE.

If needle is not a string, it is converted to an integer and applied as the ordinal value of a character.

This function is case-sensitive. For case-insensitive searches, use stristr().

Q:28 What are the differences between PHP 3 and PHP 4 and PHP 5?
A:28 Please read the release notes at http://www.php.net.

Q:29 How can we convert asp pages to PHP pages?
A:29 there are lots of tools available for asp to PHP conversion. you can search Google for that. the best one is available athttp://asp2php.naken.cc./

Q:30 What is the functionality of the function htmlentities?
A:30 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.

Q:31 How can we get second of the current time using date function?
A:31 $second = date("s");

Q:32 What is meant by urlencode and urldocode?

A:32 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.

Q:33 What is the difference between the functions unlink and unset?
A:33 unlink() deletes the given file from the file system. unset() makes a variable undefined.

Q:34 How can we register the variables into a session?
A:34 $SESSION[’name’] = “Mizan”;

Q:35 How can we get the properties (size, type, width, height) of an image using PHP image functions?
A:35 To know the Image type use exifimagetype () 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

Q:36 How can we get the browser properties using PHP?
A:36 By using $SERVER['HTTPUSERAGENT'] variable.

Q:37 What is the maximum size of a file that can be uploaded using PHP and how can we change this?
A:37 By default the maximum size is 2MB. and we can change the following setup at php.iniuploadmaxfilesize = 2M

Q:38 How can we increase the execution time of a PHP script?
A:38 by changing the following setup at php.inimaxexecutiontime = 30 ; Maximum execution time of each script, in seconds

Q:39 How can we take a backup of a MySQL table and how can we restore it. ?
A:39 To backup: BACKUP TABLE tblname[,tblname…] TO ‘/path/to/backup/directory’
RESTORE TABLE tblname[,tblname…] 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!

Q:40 How can we optimize or increase the speed of a MySQL select query?
A:40
* 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.

Q:41 How many ways can we get the value of current session id?
A:41 sessionid() returns the session id for the current session.

Q:42 How can we destroy the session, how can we unset the variable of a session?
A:42 sessionunregister — Unregister a global variable from the current session sessionunset — Free all session variables

Q:43 How can we destroy the cookie?
A:43 Set the cookie in past.

Q:44 How many ways we can pass the variable through the navigation between the pages?
A:44
* GET/QueryString
* POST

Q:45 What is the difference between eregreplace() and eregireplace()?
A:45 eregireplace() function is identical to eregreplace() except that this ignores case distinction when matching alphabetic characters.eregireplace() function is identical to eregreplace() except that this ignores case distinction when matching alphabetic characters.

Q:46 What are the different functions in sorting an array?
A:46 Sort(), arsort(), asort(), ksort(), natsort(), natcasesort(), rsort(), usort(), arraymultisort(), and uksort().

Q:47 How can we know the count/number of elements of an array?
A:47 2 ways
a) sizeof($urarray) This function is an alias of count()
b) count($urarray)

Q:48 What is the PHP predefined variable that tells the What types of
images that PHP supports?
A:48 Though i am not sure if this is wrong or not, With the exif extension you are able to work with image meta data.

Q:49 How can I know that a variable is a number or not using a JavaScript?
A:49 bool isnumeric ( 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.

Q:50 List out some tools through which we can draw E-R diagrams for mysql.
A:51 Case Studio
Smart Draw

Q:51 How can I retrieve values from one database server and store them in other database server using PHP?

A:51 we can always fetch from one database and rewrite to another. here is a nice solution of it.

$db1 = mysqlconnect(“host”,”user”,”pwd”)
mysqlselectdb(“db1″, $db1);
$res1 = mysqlquery(“query”,$db1);$db2 = mysqlconnect(“host”,”user”,”pwd”)
mysqlselectdb(“db2″, $db2);
$res2 = mysqlquery(“query”,$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
$res3 = mysqlquery(“query”,$db1); //this will failSo how to solve that?

take a look below.
$db1 = mysqlconnect(“host”,”user”,”pwd”)
mysqlselectdb(“db1″, $db1);
$res1 = mysqlquery(“query”,$db1);

$db2 = mysqlconnect(“host”,”user”,”pwd”, true)
mysqlselectdb(“db2″, $db2);
$res2 = mysqlquery(“query”,$db2);

So mysqlconnect 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);

Thanks goes to Hasan and Hasin for this solution.

Q:52 List out the predefined classes in PHP?
A:52 Directory
stdClass
__PHP_Incomplete_Class
exception
php_user_filter

Q:53 How can I make a script that can be bi-language (supports English, German)?
A:53 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.

Q:54 What are the difference between abstract class and interface?
A:54 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.

Q:55 How can we send mail using JavaScript?
A:55 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.

Q:56 How can we repair a MySQL table?
A:56 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

Q:57 What are the advantages of stored procedures, triggers, indexes?
A:57 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.

Q:58 What is the maximum length of a table name, database name, and fieldname in MySQL?
A:58 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:

Q:59 How many values can the SET function of MySQL take?
A:59 MySQL set can take zero or more values but at the maximum it can take 64 values

Q:60 What are the other commands to know the structure of table using MySQL commands except explain command?
A:60 describe Table-Name;

Q:61 How many tables will create when we create table, what are they?
A:61 The ‘.frm’ file stores the table definition.
The data file has a ‘.MYD’ (MYData) extension.
The index file has a ‘.MYI’ (MYIndex) extension,

Q:62 What is the purpose of the following files having extensions 1) .frm 2) .myd 3) .myi? What do these files contain?
A:62 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,

Q:63 What is maximum size of a database in MySQL?
A:63 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

Q:64 Give the syntax of Grant and Revoke commands?
A:64 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

Q:65 Explain Normalization concept?
A:65 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

Q:66 How can we find the number of rows in a table using MySQL?
A:66 Use this for mysql
>SELECT COUNT(*) FROM table_name;

Q:67 How can we find the number of rows in a result set using PHP?
A:67 $result = mysql_query($sql, $db_link);
$num_rows = mysql_num_rows($result);
echo "$num_rows rows found";

Q:68 How many ways we can we find the current date using MySQL?
A:68 SELECT CURDATE();
CURRENT_DATE() = CURDATE()
for time use
SELECT CURTIME();
CURRENT_TIME() = CURTIME()

Q:69 What are the advantages/disadvantages of MySQL and PHP?
A:69 Both of them are open source software (so free of cost), support cross platform. php is faster then ASP and JSP.

Q:70 What is the difference between GROUP BY and ORDER BY in Sql?
A:70 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

Q:71 What is the difference between char and varchar data types?
A:71 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 ‘mizan’, if each char takes a byte
eg. name varchar(15) will just use 5 bytes if we store ‘mizan’, if each char takes a byte. rest 10 bytes will be free.

Q:72 What is the functionality of md5 function in PHP?
A:72 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.

Q:73 How can I load data from a text file into a table?
A:73 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

Q:74 How can we know the number of days between two given dates using MySQL?
A:79 SELECT DATEDIFF(’2007-03-07′,’2005-01-01′);

Q:75 How can we know the number of days between two given dates using PHP?
A:80 $date1 = date(‘Y-m-d’);
$date2 = ’2006-08-15′;
$days = (strtotime($date1) – strtotime($date2)) / (60 * 60 * 24);

Pass a PHP Array to Javascript as JSON using AJAX and json_encode

OVERVIEW

You will mostly likely (or already have) reached a point where you have a PHP array and you need to be able to access that array from inside a Javascript function. You may wonder if it is possible to pass an array from PHP to Javascript. Fortunately I have created a tutorial on how this can be achieved. Below I will show you how to Pass a PHP Array to Javascript as JSON using AJAX. There are two parts to accomplish this task.

CREATING THE PHP ARRAY

Firstly you need a PHP script which has the PHP array you want to pass back to Javascript. You encode the array into a JSON string using the PHP function `json_encode()`. We then echo the string into the PHP file to make it accessible to the AJAX function calling this script.

CALL THE PHP SCRIPT THAT CONTAINS THE PHP ARRAY

Secondly we create an HTML which will contain the AJAX function to call the PHP script. We will use the jQuery `$.getJSON` function which converts the output from the PHP function ‘json_encode()’ into a JSON object. Once we have the JSON object, we can loop through it and use it as we require. We don’t really need to convert the JSON array to javascript array since we use jQuery’s ‘$.each()’ function to loop through the JSON array that is returned.

PASS A PHP ARRAY TO JAVASCRIPT AS JSON USING AJAX

Below is the code that is to be placed into the PHP script. This file will be called by the jQuery `$.getJSON` function.

<?php


/* set out document type to text/javascript instead of text/html */
header("Content-type: text/javascript");


/* our multidimentional php array to pass back to javascript via ajax */
$arr = array(
        array(
                "first_name" => "Darian",
                "last_name" => "Brown",
                "age" => "28",
                "email" => "darianbr@example.com"
        ),
        array(
                "first_name" => "John",
                "last_name" => "Doe",
                "age" => "47",
                "email" => "john_doe@example.com"
        )
);


/* encode the array as json. this will output [{"first_name":"Darian","last_name":"Brown","age":"28","email":"darianbr@example.com"},{"first_name":"John","last_name":"Doe","age":"47","email":"john_doe@example.com"}] */
echo json_encode($arr);


?>

JAVASCRIPT / HTML CODE SNIPPET

Place this code into a file with the extension `.html`. The below code will call the above PHP script using AJAX and the jQuery function `$.getJSON`. The PHP script will have the PHP array encoded as a json string. Once the `$.getJSON` function returns, the Javascript function will have access to the PHP array that has been converted into a JSON object.

<html>
<head>
        <script type='text/javascript' src='http://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js'></script>
</head>
<body>


        <!-- this UL will be populated with the data from the php array -->
        <ul></ul>


        <script type='text/javascript'>
        $(document).ready(function(){
                /* call the php that has the php array which is json_encoded */
                $.getJSON('json_encoded_array.php', function(data) {
                        /* data will hold the php array as a javascript object */
                        $.each(data, function(key, val) {
                                $('ul').append('<li id="' + key + '">' + val.first_name + ' ' + val.last_name + ' ' + val.email + ' ' + val.age + '</li>');
                        });
                });


        });
        </script>


</body>
</html>

PASSING VARIABLES TO PHP USING JSON AND AJAX

If you would like to pass some variables to PHP you can change the parameters as shown above. In my example below, I pass the variables name and age and then the PHP function could use these to search a database or file for that person and then return that specific information as a JSON array.

$.getJSON('json_encoded_array.php', {name:'Darian Brown',age:40}, function(data) {
        // ... handle response as above
}

HTML, JAVASCRIPT, PHP, PROGRAMMING ajax, html, javascript, json, php, programming

Abstract Classes and Interface in PHP

Abstract class and Interface in php play very important role in oop. In this section we will discuss following point

1. What is abstract classes.
2. What is interface
3. How to implement abstract classes in php
4. How to implement interface in php
5. Different between abstract classes and interface.

What is abstract Classes

As from name it seem like something that is hidden. Yes nature of the abstract classes are same. Abstract classes are those classes which can not be directly initialized. Or in other word we can say that you can not create object of abstract classes. Abstract classes always created for inheritance purpose. You can only inherit abstract class in your child class. Lots of people say that in abstract class at least your one method should be abstract. Abstract method are the method which is only defined but declared. This is not true definition as per my assumption. But your any class has at least one method abstract than your class is abstract class.

Usually abstract class are also known as base class. We call it base class because abstract class are not the class which is available directly for creating object. It can only act as parent class of any normal class. You can use abstract class in class hierarchy. Mean one abstract class can inherit another abstract class also.

Abstract classes in PHP

Abstract classes in php are simillar like other oop languages. You can create abstract classes in php using abstractkeyword. Once you will make any class abstract in php you can not create object of that class.
abstract class abc
{
public function xyz()
{
return 1;
}
}
$a = new abc();//this will throw error in php
above code will throw error in php.

Abstract classes in php are only for inheriting in other class.
abstract class testParent
{
public function abc()
{
//body of your funciton
}
}
class testChild extends testParent
{
public function xyz()
{
//body of your function
}
}
$a = new testChild();
In above example you are creating of testChild Class. TestChild class is inheriting testParent abstract class. So your abstract class is only available for inheritance. Main motive of creating abstract classes in php is to apply restriction of direct initialization or object creation.

Implementation of abstract method

As we know that abstract functions are those functions of abstract class which is only defined. It will be declared in your child class. You can create any method abstract using keyword abstract. You can only create abstract method either in abstract class or interface. Following is example of the abstract method implementation:

abstract class abc
{
abstract protected function f1($a , $b);
}
class xyz extends abc
{
protected function f1($name , $address)
{
echo "$name , $address";
}
}
$a = new xyz();

In class abc we have defined an abstract function f1. Now when we have inherited class abc then declared function f1.If you have an abstract method in your abstract class then once you inherit your abstract class then it is necessary to declare your abstract method. If you will not declare your abstract method then PHP will throw error in that case.

You can declare your abstract method in child class with the same visibility or less restricted visibility.

abstract class parentTest
{
abstract protected function f1();
abstract public function f2();
//abstract private function f3(); //this will trhow error
}
class childTest
{
public function f1()
{
//body of your function
}
public function f2()
{
//body of your function
}
protected function f3()
{
//body of your function
}
}
$a = new childTest();

In above code you can see that you have declare 3 function in abstract class. But private declaration of the abstract method will always throw error. Because private method is availabe only in the same class context. But in case of f1. This is protected. Now in child class we have defined it as public because public is less restricted than protected. And for function f2 which is already public so we have defined it as public in our child class. We have defined it public because no any visibility is less restricted than public.

What is Interface ?

Interface in oop enforce definition of some set of method in the class. By implementing interface you are forcing any class to must declaring some specific set of methods in oop. For example if you are creating class to render HTML element then it is necessary to set id and name of your html tag. So in this case you will create interface for that class and define method like setID and setName. So whenever someone will create any class to render HTML tag and implemented your interface then he must need to define setId and setName method in their class. In other word you can say that by help of interface you can set some definition of your object. Interface is very useful if you are creating architecture of any oop base application. Inter

Interface in PHP

Interface in php can be implemented like other oop lanugage. You can create interface in php using keyword interface. By implementation of interface in php class you are specifying set of the method which classes must implement.

You can create interface in php using interface keyword. Rest of the things are typically identical to classes. Following is very small example of interface in php.
interface abc
{
public function xyz($b);
}
So in above code you are creating interface with name abc. Interface abc has function xyz. Whenever you will implement abc interface in your class then you have to create method with name xyz. If you will not create function xyz then it will throw error.

You can implement your interface in your class using implements keyword. Let us implement our interface abc in our class
class test implements abc
{
public function xyz($b)
{
//your function body
}
}

You can only define method in interface with public accessibility. If you will use other than public visibility in interface then it will throw error. Also while defining method in your interface do not use abstract keyword in your methods.

You can also extend interface like class. You can extend interface in php using extends keyword.
interface template1
{
public function f1();
}
interface template2 extends template1
{
public function f2();
}
class abc implements template2
{
public function f1()
{
//Your function body
}
public function f2()
{
//your function body
}
}
So here template2 has all property of tempate2. So whenever you will implement template2 in your class, you have to create function of both interfaces.

You can also extend multiple interface in one interface in php.
interface template1
{
public function f1();
}
interface template2
{
public function f2();
}
interface template3 extends template1, template2
{
public function f3();
}
class test implements template3
{
public function f1()
{
//your function body
}
public function f2()
{
//your function body
}
public function f3()
{
//your function body
}
}

You can also implement more than one interface in php class.
interface template1
{
public function f1();
}
interface template2
{
public function f2();
}
class test implments template1, template2
{
public function f1()
{
//your function body
}
public function f2()
{
//your function body
}
}
You can not implement 2 interfaces if both share function with same name. It will throw error.

Your function parameter in class must be identical to the parameter in the interface signature. Following is example some example
interface template1
{
public function f1($a)
}
class test implements template1
{
public function f1($a)
{
echo $a;
}
}
Above will work. But following example will not work:
interface template1
{
public function f1($a)
}
class test implements template1
{
public function f1()
{
echo $a;
}
}
But it is not necessary to use the same name of the variable. Like $a. You can also use any name. For example:
interface template1
{
public function f1($a)
}
class test implements template1
{
public function f1($name)
{
echo $name;
}
}
If you are using default argument then you can change your value of the argument. For example
interface template1
{
public function f1($a = 20)
}
class test implements template1
{
public function f1($name  = "ankur")
{
echo $name;
}
}

In above section we have discussed interfaces and abstract classes in php. Both are almost doing same things but has some difference.

Differences between abstract class and interface in PHP

Following are some main difference between abstract classes and interface in php

1. In abstract classes this is not necessary that every method should be abstract. But in interface every method is abstract.
2. Multiple and multilevel both type of inheritance is possible in interface. But single and multilevel inheritance is possible in abstract classes.
3. Method of php interface must be public only. Method in abstract class in php could be public or protected both.
4. In abstract class you can define as well as declare methods. But in interface you can only defined your methods.

This article is taken from:  http://www.techflirt.com/tutorials/oop-in-php/abstract-classes-interface.html

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