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Ajay Kumar
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QUICK QUERY

What are the different types of errors in JavaScript?

There are three types of errors:

  • Load time errors: Errors which come up when loading a web page like improper syntax errors are known as Load time errors and it generates the errors dynamically.
  • Run time errors: Errors that come due to misuse of the command inside the HTML language.
  • Logical Errors: These are the errors that occur due to the bad logic performed on a function which is having different operation.

What are escape characters?

Escape characters (Backslash) is used when working with special characters like single quotes, double quotes, apostrophes and ampersands. Place backslash before the characters to make it display.

Example:

document.write "I m a "good" boy"
document.write "I m a "good" boy"

What is the difference between an alert box and a confirmation box?

An alert box displays only one button which is the OK button.

But a Confirmation box displays two buttons namely OK and cancel.

What are all the types of Pop up boxes available in JavaScript?

  • Alert
  • Confirm and
  • Prompt

Explain the difference between "==" and "==="?

"==" checks only for equality in value whereas "===" is a stricter equality test and returns false if either the value or the type of the two variables are different.

Explain how can you submit a form using JavaScript?

To submit a form using JavaScript use document.form[0].submit();

document.form[0].submit();

Explain the working of timers in JavaScript? Also elucidate the drawbacks of using the timer, if any?

Timers are used to execute a piece of code at a set time or also to repeat the code in a given interval of time. This is done by using the functions setTimeout, setInterval and clearInterval.

The setTimeout(function, delay) function is used to start a timer that calls a particular function after the mentioned delay. The setInterval(function, delay) function is used to repeatedly execute the given function in the mentioned delay and only halts when cancelled. The clearInterval(id) function instructs the timer to stop.

Timers are operated within a single thread, and thus events might queue up, waiting to be executed.

Which symbol is used for comments in Javascript?

// for Single line comments and

/* Multi

Line

Comment

*/

How to use external JavaScript file?

I am assuming that js file name is message.js, place the following script tag inside the head tag.

<script type="text/javascript" src="message.js"></script>

How to write a hello world example of JavaScript?

A simple example of JavaScript hello world is given below. You need to place it inside the body tag of HTML.

<script type="text/javascript">  
document.write("JavaScript Hello World!");  
</script> 

What is the difference between JavaScript and JScript?

Netscape provided the JavaScript language. Microsoft changed the name and called it JScript to avoid the trademark issue. In other words, you can say JScript is the same as JavaScript, but Microsoft provides it.

Define a named function in JavaScript.

The function which has named at the time of definition is called a named function. For example

function msg()  
{  
  document.write("Named Function");  
}  
msg(); 

List some of the disadvantages of JavaScript.

Some of the disadvantages of JavaScript are:

  • No support for multithreading
  • No support for multiprocessing
  • Reading and writing of files is not allowed
  • No support for networking applications.

List some of the advantages of JavaScript.

Some of the advantages of JavaScript are:

  • Server interaction is less
  • Feedback to the visitors is immediate
  • Interactivity is high
  • Interfaces are richer

List some features of JavaScript.

Some of the features of JavaScript are:

 
 
 
 
 
 
 
 
Volume 0%
 
 
  • Lightweight
  • Interpreted programming language
  • Good for the applications which are network-centric
  • Complementary to Java
  • Complementary to HTML
  • Open source
  • Cross-platform

What is JavaScript?

JavaScript is a scripting language. It is different from Java language. It is object-based, lightweight, cross-platform translated language. It is widely used for client-side validation. The JavaScript Translator (embedded in the browser) is responsible for translating the JavaScript code for the web browser.

How MySQL Optimizes DISTINCT?

DISTINCT is converted to a GROUP BY on all columns and it will be combined with ORDER BY clause.

 
SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;

What are the column comparisons operators?

The = , <>, <=, <, >=, >,<<,>>, <=>, AND, OR, or LIKE operators are used in column comparisons in SELECT statements.

Differentiate CHAR_LENGTH and LENGTH?

CHAR_LENGTH  is character count whereas the LENGTH is byte count. The numbers are same for Latin characters but they are different for Unicode and other encodings.

What are DDL, DML, and DCL?

Majorly SQL commands can be divided into three categories, i.e., DDL, DML & DCL. Data Definition Language (DDL) deals with all the database schemas, and it defines how the data should reside in the database. Commands like CreateTABLE and ALTER TABLE are part of DDL.

Data Manipulative Language (DML) deals with operations and manipulations on the data. The commands in DML are Insert, Select, etc.

Data Control Languages (DCL) are related to the Grant and permissions. In short, the authorization to access any part of the database is defined by these.

What are the drivers in MySQL?

Following are the drivers available in MySQL:

  • PHP Driver
  • JDBC Driver
  • ODBC Driver
  • C WRAPPER
  • PYTHON Driver
  • PERL Driver
  • RUBY Driver
  • CAP11PHP Driver
  • Ado.net5.mxz

What is the difference between primary key and candidate key?

To identify each row of a table, we will use a primary key. For a table, there exists only one primary key.

A candidate key is a column or a set of columns, which can be used to uniquely identify any record in the database without having to reference any other data.

What are federated tables?

Federated tables are tables that point to the tables located on other databases on some other server.

What is the usage of the "i-am-a-dummy" flag in MySQL?

In MySQL, the "i-am-a-dummy" flag makes the MySQL engine to deny the UPDATE and DELETE commands unless the WHERE clause is present.

What is the usage of regular expressions in MySQL?

In MySQL, regular expressions are used in queries for searching a pattern in a string.

  • * Matches 0 more instances of the string preceding it.
  • + matches one more instances of the string preceding it.
  • ? Matches 0 or 1 instances of the string preceding it.
  • . Matches a single character.
  • [abc] matches a or b or z
  • | separates strings
  • ^ anchors the match from the start.
  • "." Can be used to match any single character. "|" can be used to match either of the two strings
  • REGEXP can be used to match the input characters with the database.

Example:

The following statement retrieves all rows where column employee_name contains the text 1000 (example salary):

Select employee_name    
From employee    
Where employee_name REGEXP '1000'    
Order by employee_name   

What is MySQL data directory?

MySQL data directory is a place where MySQL stores its data. Each subdirectory under this data dictionary represents a MySQL database. By default, the information managed my MySQL = server mysqld is stored in the data directory.

What is the use of mysql_close()?

Mysql_close() cannot be used to close the persistent connection. However, it can be used to close a connection opened by mysql_connect().

What are the differences between MySQL_fetch_array(), MySQL_fetch_object(), MySQL_fetch_row()?

Mysql_fetch_object is used to retrieve the result from the database as objects, while mysql_fetch_array returns result as an array. This will allow access to the data by the field names.

For example:

Using mysql_fetch_object field can be accessed as $result->name.

Using mysql_fetch_array field can be accessed as $result->[name].

Using mysql_fetch_row($result) where $result is the result resource returned from a successful query executed using the mysql_query() function.

 

What are the advantages of MyISAM over InnoDB?

MyISAM follows a conservative approach to disk space management and stores each MyISAM table in a separate file, which can be further compressed if required. On the other hand, InnoDB stores the tables in the tablespace. Its further optimization is difficult.

How is the MyISAM table stored?

MyISAM table is stored on disk in three formats.

  • '.frm' file : storing the table definition
  • '.MYD' (MYData): data file
  • '.MYI' (MYIndex): index file

Write a query to select all teams that won either 1, 3, 5, or 7 games.

SELECT team_name FROM team WHERE team_won IN (1, 3, 5, 7);

Write a query to count the number of rows of a table in MySQL.

SELECT COUNT user_id FROM users;

What is the query to display the top 20 rows?

SELECT * FROM table_name LIMIT 0,20;

What is the difference between NOW() and CURRENT_DATE()?

NOW() command is used to show current year, month, date with hours, minutes, and seconds while CURRENT_DATE() shows the current year with month and date only.

Write a query to display the current date and time?

If you want to display the current date and time, use -

SELECT NOW();

If you want to display the current date only, use:

SELECT CURRENT_DATE();

How many columns can you create for an index?

You can a create maximum of 16 indexed columns for a standard table.

What is REGEXP?

REGEXP is a pattern match using a regular expression. The regular expression is a powerful way of specifying a pattern for a sophisticated search.

Basically, it is a special text string for describing a search pattern. To understand it better, you can think of a situation of daily life when you search for .txt files to list all text files in the file manager. The regex equivalent for .txt will be .*.txt.

How to display the nth highest salary from a table in a MySQL query?

Let us take a table named the employee.

To find Nth highest salary is:

select distinct(salary)from employee order by salary desc limit n-1,1

if you want to find 3rd largest salary:

select distinct(salary)from employee order by salary desc limit 2,1

What does "i_am_a_dummy flag" do in MySQL?

The "i_am_a_dummy flag" enables the MySQL engine to refuse any UPDATE or DELETE statement to execute if the WHERE clause is not present. Hence it can save the programmer from deleting the entire table my mistake if he does not use WHERE clause.

What is the difference between MySQL_connect and MySQL_pconnect?

Mysql_connect:

  1. It opens a new connection to the database.
  2. Every time you need to open and close the database connection, depending on the request.
  3. Opens page whenever it is loaded.

Mysql_pconnect:

  1. In Mysql_pconnect, "p" stands for persistent connection, so it opens the persistent connection.
  2. The database connection cannot be closed.
  3. It is more useful if your site has more traffic because there is no need to open and close connection frequently and whenever the page is loaded.

What is the difference between CHAR and VARCHAR?

  1. CHAR and VARCHAR have differed in storage and retrieval.
  2. CHAR column length is fixed, while VARCHAR length is variable.
  3. The maximum no. of character CHAR data types can hold is 255 characters, while VARCHAR can hold up to 4000 characters.
  4. CHAR is 50% faster than VARCHAR.
  5. CHAR uses static memory allocation, while VARCHAR uses dynamic memory allocation.

What are the disadvantages of MySQL?

  1. MySQL is not so efficient for large scale databases.
  2. It does not support COMMIT and STORED PROCEDURES functions version less than 5.0.
  3. Transactions are not handled very efficiently.
  4. The functionality of MySQL is highly dependent on other addons.
  5. Development is not community-driven.

What are the advantages of MySQL in comparison to Oracle?

  1. MySQL is a free, fast, reliable, open-source relational database while Oracle is expensive, although they have provided Oracle free edition to attract MySQL users.
  2. MySQL uses only just under 1 MB of RAM on your laptop, while Oracle 9i installation uses 128 MB.
  3. MySQL is great for database enabled websites while Oracle is made for enterprises.
  4. MySQL is portable.

What is the difference between FLOAT and DOUBLE?

FLOAT stores floating-point numbers with accuracy up to 8 places and allocate 4 bytes. On the other hand, DOUBLE stores floating-point numbers with accuracy up to 18 places and allocates 8 bytes.

What is the difference between the heap table and the temporary table?

Heap tables:

Heap tables are found in memory that is used for high-speed storage temporarily. They do not allow BLOB or TEXT fields.

Heap tables do not support AUTO_INCREMENT.

Indexes should be NOT NULL.

Temporary tables:

The temporary tables are used to keep the transient data. Sometimes it is beneficial in cases to hold temporary data. The temporary table is deleted after the current client session terminates.

Main differences:

The heap tables are shared among clients, while temporary tables are not shared.

Heap tables are just another storage engine, while for temporary tables, you need a special privilege (create temporary table).

What is BLOB and TEXT in MySQL?

BLOB is an acronym that stands for a large binary object. It is used to hold a variable amount of data.

There are four types of the BLOB.

  1. TINYBLOB
  2. BLOB
  3. MEDIUMBLOB
  4. LONGBLOB

The differences among all these are the maximum length of values they can hold.

TEXT is a case-insensitive BLOB. TEXT values are non-binary strings (character string). They have a character set, and values are stored and compared based on the collation of the character set.

There are four types of TEXT.

  1. TINYTEXT
  2. TEXT
  3. MEDIUMTEXT
  4. LONGTEXT

What is the heap table?

Tables that are present in memory is known as HEAP tables. When you create a heap table in MySQL, you should need to specify the TYPE as HEAP. These tables are commonly known as memory tables. They are used for high-speed storage on a temporary basis. They do not allow BLOB or TEXT fields.

What is a trigger in MySQL?

A trigger is a set of codes that executes in response to some events.

How many Triggers are possible in MySQL?

There are only six Triggers allowed to use in the MySQL database.

  1. Before Insert
  2. After Insert
  3. Before Update
  4. After Update
  5. Before Delete
  6. After Delete

What is the difference between TRUNCATE and DELETE in MySQL?

  • TRUNCATE is a DDL command, and DELETE is a DML command.
  • It is not possible to use Where command with TRUNCATE QLbut you can use it with DELETE command.
  • TRUNCATE cannot be used with indexed views, whereas DELETE can be used with indexed views.
  • The DELETE command is used to delete data from a table. It only deletes the rows of data from the table while truncate is a very dangerous command and should be used carefully because it deletes every row permanently from a table.

How to view the database in MySQL?

Working with the MySQL server, it is a common task to view or list the available databases. We can view all the databases on the MySQL server host using the following command:

SHOW DATABASES; 

How does indexing works in MySQL?

Indexing is a process to find an unordered list into an ordered list. It helps in maximizing the query's efficiency while searching on tables in MySQL. The working of MySQL indexing is similar to the book index.

Suppose we have a book and want to get information about, say, searching. Without indexing, it is required to go through all pages one by one, until the specific topic was not found. On the other hand, an index contains a list of keywords to find the topic mentioned on pages. Then, we can flip to those pages directly without going through all pages.

How to join three tables in MySQL?

Sometimes we need to fetch data from three or more tables. There are two types available to do these types of joins. Suppose we have three tables named Student, Marks, and Details.

Let's say Student has (stud_id, name) columns, Marks has (school_id, stud_id, scores) columns, and Details has (school_id, address, email) columns.

1. Using SQL Join Clause

This approach is similar to the way we join two tables. The following query returns result from three tables:

SELECT name, scores, address, email FROM Student s   
INNER JOIN Marks m on s.stud_id = m.stud_id   
INNER JOIN Details d on d.school_id = m.school_id; 

2. Using Parent-Child Relationship

It is another approach to join more than two tables. In the above tables, we have to create a parent-child relationship. First, create column X as a primary key in one table and as a foreign key in another table. Therefore, stud_id is the primary key in the Student table and will be a foreign key in the Marks table. Next, school_id is the primary key in the Marks table and will be a foreign key in the Details table. The following query returns result from three tables:

 

SELECT name, scores, address, email   
FROM Student s, Marks m, Details d   
WHERE s.stud_id = m.stud_id AND m.school_id = d.school_id;

What is MySQL Inner Join ?

MySQL Inner Join

The MySQL Inner Join is used to returns only those results from the tables that match the specified condition and hides other rows and columns. MySQL assumes it as a default Join, so it is optional to use the Inner Join keyword with the query.

We can understand it with the following visual representation where Inner Joins returns only the matching results from table1 and table2:

 

MySQL Inner Join Syntax:
The Inner Join keyword is used with the SELECT statement and must be written after the FROM clause. The following syntax explains it more clearly:

SELECT columns  
FROM table1  
INNER JOIN table2 ON condition1  
INNER JOIN table3 ON condition2  
...; 

MySQL Inner Join Example

Let us first create two tables "students" and "technologies" that contains the following data:

Table: student

MySQL Inner Join

Table: technologies

MySQL Inner Join

To select records from both tables, execute the following query:

SELECT students.stud_fname, students.stud_lname, students.city, technologies.technology    
FROM students   
INNER JOIN technologies    
ON students.student_id = technologies.tech_id;

After successful execution of the query, it will give the following output:

MySQL Inner Join

How to join two tables in MySQL?

We can connect two or more tables in MySQL using the JOIN clause. MySQL allows various types of JOIN clauses. These clauses connect multiple tables and return only those records that match the same value and property in all tables. The following are the four easy ways to join two or more tables in MySQL:

  • Inner Join
  • Left Join
  • Right Join
  • Cross Join

How to delete a row in MySQL?

We can delete a row from the MySQL table using the DELETE STATEMENT within the database. The following is the generic syntax of DELETE statement in MySQL to remove one or more rows from a table:

DELETE FROM table_name WHERE Condition_specified; 

How to insert data in MySQL?

We can insert data in a MySQL table using the INSERT STATEMENT. This statement allows us to insert single or multiple rows into a table. The following is the basic syntax to insert a record into a table:

INSERT INTO table_name ( field1, field2,...fieldN )    
VALUES  ( value1, value2,...valueN );    


If we want to insert more than one rows into a table, use the below syntax:

INSERT INTO table(field1, field2,...fieldN)  
VALUES   
   (value1, value 2, ...),  
   (value1, value2, ...),  
    ...  
   (value1, value2, ...); 

How to delete columns in MySQL?

We can remove, drop, or delete one or more columns in an existing table using the ALTER TABLE statement as follows:

 

ALTER TABLE table_name DROP COLUMN column_name1, column_name2....; 

How to change the column name in MySQL?

While creating a table, we have kept one of the column names incorrectly. To change or rename an existing column name in MySQL, we need to use the ALTER TABLE and CHANGE commands together. The following are the syntax used to rename a column in MySQL:

ALTER TABLE table_name     
    CHANGE COLUMN old_column_name new_column_name column_definition [FIRST|AFTER existing_column];  

 

How to delete a table in MySQL?

We can delete a table in MySQL using the Drop Table statement. This statement removes the complete data of a table, including structure and definition from the database permanently. Therefore, it is required to be careful while deleting a table. After using the statement, we cannot recover the table in MySQL. The statement is as follows:

DROP TABLE  table_name;   

How to add columns in MySQL?

A column is a series of cells in a table that stores one value for each row in a table. We can add columns in an existing table using the ALTER TABLE statement as follows:

ALTER TABLE table_name     
    ADD COLUMN column_name column_definition [FIRST|AFTER existing_column]; 

What are the different tables present in MySQL?

There are many tables that remain present by default. But, MyISAM is the default database engine used in MySQL. There are five types of tables that are present:

  • MyISAM
  • Heap
  • Merge
  • INNO DB
  • ISAM

Why do we use the MySQL database server?

irst of all, the MYSQL server is free to use for developers and small enterprises.

MySQL server is open source.

MySQL's community is tremendous and supportive; hence any help regarding MySQL is resolved as soon as possible.

MySQL has very stable versions available, as MySQL has been in the market for a long time. All bugs arising in the previous builds have been continuously removed, and a very stable version is provided after every update.

The MySQL database server is very fast, reliable, and easy to use. You can easily use and modify the software. MySQL software can be downloaded free of cost from the internet.

What is the default port for MySQL Server?

The default port for MySQL server is 3306.

What is the difference between the database and the table?

There is a major difference between a database and a table. The differences are as follows:

  • Tables are a way to represent the division of data in a database while the database is a collection of tables and data.
  • Tables are used to group the data in relation to each other and create a dataset. This dataset will be used in the database. The data stored in the table in any form is a part of the database, but the reverse is not true.
  • A database is a collection of organized data and features used to access them, whereas the table is a collection of rows and columns used to store the data.

What are the technical specifications of MySQL?

MySQL has the following technical specifications -

  • Flexible structure
  • High performance
  • Manageable and easy to use
  • Replication and high availability
  • Security and storage management
  • Drivers
  • Graphical Tools
  • MySQL Enterprise Monitor
  • MySQL Enterprise Security
  • JSON Support
  • Replication & High-Availability
  • Manageability and Ease of Use
  • OLTP and Transactions
  • Geo-Spatial Support

What is the difference between MySQL and SQL?

SQL is known as the standard query language. It is used to interact with the database like MySQL. MySQL is a database that stores various types of data and keeps it safe.

A PHP script is required to store and retrieve the values inside the database.

SQL is a computer language, whereas MySQL is a software or an application

SQL is used for the creation of database management systems whereas MySQL is used to enable data handling, storing, deleting and modifying data

In which language MySQL has been written?

MySQL is written in C and C++, and its SQL parser is written in yacc.

What is MySQL?

MySQL is a multithreaded, multi-user SQL database management system which has more than 11 million installations. It is the world's second most popular and widely-used open source database. It is interesting how MySQL name was given to this query language. The term My is coined by the name of the daughter of co-founder Michael Widenius's daughter, and SQL is the short form of Structured Query Language. Using MySQL is free of cost for the developer, but enterprises have to pay a license fee to Oracle.

Formerly MySQL was initially owned by a for-profit firm MySQL AB, then Sun Microsystems bought it, and then Oracle bought Sun Microsystems, so Oracle currently owns MySQL.

MySQL is an Oracle-supported Relational Database Management System (RDBMS) based on structured query language. MySQL supports a wide range of operating systems, most famous of those include Windows, Linux & UNIX. Although it is possible to develop a wide range of applications with MySQL, it is only used for web applications & online publishing. It is a fundamental part of an open-source enterprise known as Lamp.

What is the Importance of Parser in PHP?

PHP parser parses the PHP developed website from the opening to the closing tag. Tags indicate that from where PHP code is being started and ended. In other words, opening and closing tags decide the scope of PHP scripting syntax of closing tag in PHP

<?php syntax of opening tag in PHP
?> syntax of closing tag in PHP

What is the purpose of $_SERVER variable in PHP?

$_SERVER − This is an array containing information such as headers, paths, and script locations. The entries in this array are created by the web server. There is no guarantee that every web server will provide any of these. 

<!DOCTYPE html>
<html>
<body>


echo $_SERVER['PHP_SELF'];
echo "
"
;
echo $_SERVER['SERVER_NAME'];
echo "
"
;
echo $_SERVER['HTTP_HOST'];
echo "
"
;
echo $_SERVER['HTTP_REFERER'];
echo "
"
;
echo $_SERVER['HTTP_USER_AGENT'];
echo "
"
;
echo $_SERVER['SCRIPT_NAME'];
?>


</body>
</html>

The following table lists the most important elements that can go inside $_SERVER:

Element/Code Description
$_SERVER['PHP_SELF'] Returns the filename of the currently executing script
$_SERVER['GATEWAY_INTERFACE'] Returns the version of the Common Gateway Interface (CGI) the server is using
$_SERVER['SERVER_ADDR'] Returns the IP address of the host server
$_SERVER['SERVER_NAME'] Returns the name of the host server (such as www.sstechlab.com)
$_SERVER['SERVER_SOFTWARE'] Returns the server identification string (such as Apache/2.2.24)
$_SERVER['SERVER_PROTOCOL'] Returns the name and revision of the information protocol (such as HTTP/1.1)
$_SERVER['REQUEST_METHOD'] Returns the request method used to access the page (such as POST)
$_SERVER['REQUEST_TIME'] Returns the timestamp of the start of the request (such as 1377687496)
$_SERVER['QUERY_STRING'] Returns the query string if the page is accessed via a query string
$_SERVER['HTTP_ACCEPT'] Returns the Accept header from the current request
$_SERVER['HTTP_ACCEPT_CHARSET'] Returns the Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
$_SERVER['HTTP_HOST'] Returns the Host header from the current request
$_SERVER['HTTP_REFERER'] Returns the complete URL of the current page (not reliable because not all user-agents support it)
$_SERVER['HTTPS'] Is the script queried through a secure HTTP protocol
$_SERVER['REMOTE_ADDR'] Returns the IP address from where the user is viewing the current page
$_SERVER['REMOTE_HOST'] Returns the Host name from where the user is viewing the current page
$_SERVER['REMOTE_PORT'] Returns the port being used on the user's machine to communicate with the web server
$_SERVER['SCRIPT_FILENAME'] Returns the absolute pathname of the currently executing script
$_SERVER['SERVER_ADMIN'] Returns the value given to the SERVER_ADMIN directive in the web server configuration file (if your script runs on a virtual host, it will be the value defined for that virtual host) (such as [email protected])
$_SERVER['SERVER_PORT'] Returns the port on the server machine being used by the web server for communication (such as 80)
$_SERVER['SERVER_SIGNATURE'] Returns the server version and virtual host name which are added to server-generated pages
$_SERVER['PATH_TRANSLATED'] Returns the file system based path to the current script
$_SERVER['SCRIPT_NAME'] Returns the path of the current script
$_SERVER['SCRIPT_URI'] Returns the URI of the current page

 

What is the purpose of $_FILES variable in PHP?

This is a global PHP variable. This variable is an associate double dimension array and keeps all the information related to uploaded file.

How will you unset a single session variable?

Here is the example to unset a single variable −

<?php
   unset($_SESSION['counter']);
?>

What is the difference between single quoted string and double quoted string?

Singly quoted strings are treated almost literally, whereas doubly quoted strings replace variables with their values as well as specially interpreting certain character sequences.

<?php
$variable = "name";
$literally = 'My $variable will not print!\n';
print($literally);
print "<br />";
$literally = "My $variable will print!\n";
print($literally);
?>

This will produce following result −

My $variable will not print!

My name will print

What is the purpse $_REQUEST variable?

The PHP $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE. We will discuss $_COOKIE variable when we will explain about cookies. The PHP $_REQUEST variable can be used to get the result from form data sent with both the GET and POST methods.

What are the differences between PHP constants and variables?

  • There is no need to write a dollar sign ($) before a constant, where as in Variable one has to write a dollar sign.

  • Constants cannot be defined by simple assignment, they may only be defined using the define() function.

  • Constants may be defined and accessed anywhere without regard to variable scoping rules.

  • Once the Constants have been set, may not be redefined or undefined.

How will you define a constant in PHP?

To define a constant you have to use define() function and to retrieve the value of a constant, you have to simply specifying its name. Unlike with variables, you do not need to have a constant with a $.

As indicated by the name, this function will return the value of the constant. This is useful when you want to retrieve value of a constant, but you do not know its name, i.e. It is stored in a variable or returned by a function.

<?php
define("MINSIZE", 50);
echo MINSIZE;
echo constant("MINSIZE"); // same thing as the previous line
?>

Only scalar data (boolean, integer, float and string) can be contained in constants.

What is NULL?

NULL is a special type that only has one value: NULL. To give a variable the NULL value, simply assign it like this −

$my_var = NULL;

The special constant NULL is capitalized by convention, but actually it is case insensitive; you could just as well have typed −

$my_var = null;

A variable that has been assigned NULL has the following properties:

It evaluates to FALSE in a Boolean context.

It returns FALSE when tested with IsSet() function.

What are the different types of PHP variables?

PHP has a total of eight data types which we use to construct our variables −

  • Integers − are whole numbers, without a decimal point, like 4195.

  • Doubles − are floating-point numbers, like 3.14159 or 49.1.

  • Booleans − have only two possible values either true or false.

  • NULL − is a special type that only has one value: NULL.

  • Strings − are sequences of characters, like 'PHP supports string operations.'

  • Arrays − are named and indexed collections of other values.

  • Objects − are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.

  • Resources − are special variables that hold references to resources external to PHP (such as database connections).

How failures in execution are handled with include() and require() functions?

If the function require() cannot access the file then it ends with a fatal error. However, the include() function gives a warning, and the PHP script continues to execute.

Is PHP a strongly typed language?

Answer: No. PHP is a weakly typed or loosely typed language.

This means PHP does not require to declare data types of the variable when you declare any variable like the other standard programming languages C# or Java. When you store any string value in a variable, then the data type is the string and if you store a numeric value in that same variable then the data type is an Integer.

Sample code:

$var = "Hello"; //String
$var = 10; //Integer

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How can we create a database using PHP and MySQL?

The necessary steps to create a MySQL database using PHP are:

  • Establish a connection to MySQL server from your PHP script.
  • If the connection is successful, write a SQL query to create a database and store it in a string variable.
  • Execute the query.

What is the Importance of Parser in PHP?

PHP parser parses the PHP developed website from the opening to the closing tag. Tags indicate that from where PHP code is being started and ended. In other words, opening and closing tags decide the scope of PHP scripting syntax of closing tag in PHP

<?php syntax of opening tag in PHP
?> syntax of closing tag in PHP

What is Cookies? How to create cookies in PHP?

A cookie is used to identify a user. A cookie is a little record that the server installs on the client's Computer. Each time a similar PC asks for a page with a program, it will send the cookie as well. With PHP, you can both make and recover cookie value.

Some important points regarding Cookies:

  1. Cookies maintain the session id generated at the back end after verifying the user's identity in encrypted form, and it must reside in the browser of the machine
  2. You can store only string values not object because you can't access any object across the website or web apps
  3. Scope: - Multiple pages.
  4. By default, cookies are temporary and transitory cookie saves in the browser only.
  5. By default, cookies are URL particular means Gmail isn't supported in Yahoo and the vice versa.
  6. Per site 20 cookies can be created in one website or web app
  7. The Initial size of the cookie is 50 bytes.
  8. The Maximum size of the cookie is 4096 bytes.

What are include() and require() functions?

The Include() function is used to put data of one PHP file into another PHP file. If errors occur, then the include() function produces a warning but does not stop the execution of the script, and it will continue to execute.

The Require() function is also used to put data of one PHP file to another PHP file. If there are any errors, then the require() function produces a warning and a fatal error and stops the script.

What is the meaning of a Persistent Cookie?

A persistent cookie is permanently stored in a cookie file on the browser's computer. By default, cookies are temporary and are erased if we close the browser.

How can we get IP address of a client in PHP?

  1. $_SERVER["REMOTE_ADDR"];  

Explain PHP split() function.

The PHP split() function splits string into an array by regular expression.

Explain PHP explode() function.

The PHP explode() function breaks a string into an array.

What is htaccess in PHP?

The .htaccess is a configuration file on Apache server. You can change configuration settings using directives in Apache configuration files like .htaccess and httpd.conf.

What are the encryption functions in PHP?

CRYPT() and MD5()

How to stop the execution of PHP script?

The exit() function is used to stop the execution of PHP script.

What are the different types of errors in PHP?

There are 3 types of error in PHP.

  1. Notices:These are non-critical errors. These errors are not displayed to the users.
  2. Warnings:These are more serious errors, but they do not result in script termination. By default, these errors are displayed to the user.
  3. Fatal Errors:These are the most critical errors. These errors may cause due to immediate termination of script.

How can we increase execution time of a PHP script?

By default, the maximum execution time for PHP scripts is set to 30 seconds. If a script takes more than 30 seconds, PHP stops the script and returns an error.

You can change the script run time by changing the max_execution_time directive in the php.ini file.

When a script is called, set_time_limit function restarts the timeout counter from zero. It means, if default timer is set to 30 sec, and 20 sec is specified in function set_time_limit(), then script will run for 45 seconds. If 0sec is specified in this function, script takes unlimited time.

How to create database connection and query in PHP?

Since PHP 4.3, mysql_reate_db() is deprecated. Now you can use the following 2 alternatives.

  • mysqli_query()
  • PDO::_query()

How to create connection in PHP?

The mysqli_connect() function is used to create a connection in PHP.

  1. resource mysqli_connect (server, username, password)    

How do you connect MySQL database with PHP?

There are two methods to connect MySQL database with PHP. Procedural and object-oriented style.

How can you send email in PHP?

The mail() function is used to send email in PHP.

  1. bool mail($to,$subject,$message,$header); 

How to download file in PHP?

The readfile() function is used to download the file in PHP.

  1. int readfile ( string $filename ) 

How to upload file in PHP?

The move_uploaded_file() function is used to upload file in PHP.

  1. bool move_uploaded_file ( string $filename , string $destination )    

What is the method to execute a PHP script from the command line?

You should just run the PHP command line interface (CLI) and specify the file name of the script to be executed as follows.

How to delete file in PHP?

The unlink() function is used to delete a file in PHP.

  1. bool unlink (string $filename)      

How to write in a file in PHP?

PHP fwrite() and fputs() functions are used to write data into file. To write data into a file, you need to use w, r+, w+, x, x+, c or c+ mode.

How to read a file in PHP?

PHP provides various functions to read data from the file. Different functions allow you to read all file data, read data line by line, and read data character by character.

PHP file read functions are given below:

  • fread()
  • fgets()
  • fgetc()

Write syntax to open a file in PHP?

PHP fopen() function is used to open file or URL and returns resource. It accepts two arguments: $filename and $mode.

Syntax:

  1. resource fopen ( string $filename , string $mode [, bool $use_include_path = false [, resource $context ]] )  

What is the difference between session and cookie?

The main difference between session and cookie is that cookies are stored on user's computer in the text file format while sessions are stored on the server side.

Cookies can't hold multiple variables, on the other hand, Session can hold multiple variables.

You can manually set an expiry for a cookie, while session only remains active as long as browser is open.

What is PHP session_start() and session_destroy() function?

PHP session_start() function is used to start the session. It starts new or resumes the current session. It returns the current session if the session is created already. If the session is not available, it creates and returns new sessions.

What is the method to register a variable into a session?

  1. <?php  
  2. Session_register($ur_session_var);  
  3. ?>  

What is a session?

PHP Engine creates a logical object to preserve data across subsequent HTTP requests, which is known as session.

Sessions generally store temporary data to allow multiple PHP pages to offer a complete functional transaction for the same user.

Simply, it maintains data of an user (browser).

How can you retrieve a cookie value?

  1. echo $_COOKIE ["user"];  

Explain setcookie() function in PHP?

PHP setcookie() function is used to set cookie with HTTP response. Once the cookie is set, you can access it by $_COOKIE superglobal variable.

Syntax:

  1. bool setcookie ( string $name [, string $value [, int $expire = 0 [, string $path     
  2. [, string $domain [, bool $secure = false [, bool $httponly = false ]]]]]] )  

Differentiate between require and include?

Require and include both are used to include a file, but if data is not found include sends warning whereas require sends Fatal error.

What are the ways to include file in PHP?

PHP allows you to include file so that page content can be reused again. There are two ways to add the file in PHP.

  1. include
  2. require

How can you submit a form without a submit button?

You can use JavaScript submit() function to submit the form without explicitly clicking any submit button.

What are the methods to submit form in PHP?

There are two methods GET and POST.

Explain some of the PHP string functions?

There are many array functions in PHP:

  • strtolower()
  • strtoupper()
  • ucfirst()
  • lcfirst()
  • ucwords()
  • strrev()
  • strlen()

How to get the length of string?

The strlen() function is used to get the length of the string.

What is the difference between indexed and associative array?

The indexed array holds elements in an indexed form which is represented by number starting from 0 and incremented by 1. For example:

  1. $season=array("summer","winter","spring","autumn");    
  2. The associative array holds elements with name. For example:

    1. $salary=array("Sonoo"=>"350000","John"=>"450000","Kartik"=>"200000");    

Explain some of the PHP array functions?

There are many array functions in PHP:

  • array()
  • array_change_key_case()
  • array_chunk()
  • count()
  • sort()
  • array_reverse()
  • array_search()
  • array_intersect()

How many types of array are there in PHP?

There are three types of array in PHP:

  1. Indexed array: an array with a numeric key.
  2. Associative array: an array where each key has its specific value.
  3. Multidimensional array: an array containing one or more arrays within itself.

What is the array in PHP?

An array is used to store multiple values in a single value. In PHP, it orders maps of pairs of keys and values. It saves the collection of the data type.

What does isset() function?

The isset() function checks if the variable is defined and not null.

hat is the use of header() function in PHP?

The header() function is used to send a raw HTTP header to a client. It must be called before sending the actual output. For example, you can't print any HTML element before using this function.

What is the use of count() function in PHP?

The PHP count() function is used to count total elements in the array, or something an object.

What are magic constants in PHP?

PHP magic constants are predefined constants, which change based on their use. They start with a double underscore (__) and end with a double underscore (__).

How a variable is declared in PHP?

A PHP variable is the name of the memory location that holds data. It is temporary storage.

Syntax:

 
  1. $variableName=value;

Which programming language does PHP resemble to?

PHP has borrowed its syntax from Perl and C.

What are the popular frameworks in PHP?

  • Laravel
  • CodeIgniter
  • Yii 2
  • CakePHP
  • Symfony
  • Zend Framework etc.

What are the popular Content Management Systems (CMS) in PHP?

  • WordPress: WordPress is a free and open-source content management system (CMS) based on PHP & MySQL. It includes a plug-in architecture and template system. It is mostly connected with blogging but supports another kind of web content, containing more traditional mailing lists and forums, media displays, and online stores.
  • Joomla: Joomla is a free and open-source content management system (CMS) for distributing web content, created by Open Source Matters, Inc. It is based on a model-view-controller web application framework that can be used independently of the CMS.
  • Magento: Magento is an open source E-trade programming, made by Varien Inc., which is valuable for online business. It has a flexible measured design and is versatile with many control alternatives that are useful for clients. Magento utilizes E-trade stage which offers organization extreme E-business arrangements and extensive support network.
  • Drupal: Drupal is a CMS platform developed in PHP and distributed under the GNU (General Public License).

What does the scope of variables mean?

The scope of a variable is the context within which it is defined. For the most part, all PHP variables only have a single scope. This single scope spans included and required files as well.

What does $_COOKIE mean?

$_COOKIE is an associative array of variables sent to the current PHP script using the HTTP Cookies

What does $_ENV mean?

$_ENV is an associative array of variables sent to the current PHP script via the environment method.

What does $_FILES means?

$_FILES is an associative array composed of items sent to the current script via the HTTP POST method.

What does $_SERVER mean?

$_SERVER is an array including information created by the web server such as paths, headers, and script locations.

What is the difference between session_unregister() and session_unset()?

The session_unregister() function unregister a global variable from the current session and the session_unset() function frees all session variables.

When do sessions end?

Sessions automatically end when the PHP script finishes executing but can be manually ended using the session_write_close().

How can you propagate a session id?

You can propagate a session id via cookies or URL parameters.

How to initiate a session in PHP?

The use of the function session_start() lets us activating a session.

what is the definition of a session?

A session is a logical object enabling us to preserve temporary data across multiple PHP pages.

Are Parent constructors called implicitly inside a class constructor?

No, a parent constructor have to be called explicitly as follows:

parent::constructor($value)

In PHP, objects are they passed by value or by reference?

In PHP, objects passed by value.

What does the unset() function mean?

The unset() function is dedicated for variable management. It will make a variable undefined.

How be the result set of Mysql handled in PHP?

The result set can be handled using mysqli_fetch_array, mysqli_fetch_assoc, mysqli_fetch_object or mysqli_fetch_row.

What type of operation is needed when passing values through a form or an URL?

If we would like to pass values through a form or an URL, then we need to encode and to decode them using htmlspecialchars() and urlencode().

How is the comparison of objects done in PHP?

We use the operator '==' to test is two objects are instanced from the same class and have same attributes and equal values. We can test if two objects are referring to the same instance of the same class by the use of the identity operator '==='.

What is the meaning of a final class and a final method?

'final' is introduced in PHP5. Final class means that this class cannot be extended and a final method cannot be overridden.

Is multiple inheritance supported in PHP?

PHP supports only single inheritance; it means that a class can be extended from only one single class using the keyword 'extended'.

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

The $var (single dollar) is a normal variable with the name var that stores any value like string, integer, float, etc.

The $$var (double dollar) is a reference variable that stores the value of the $variable inside it.

How a variable is declared in PHP?

A PHP variable is the name of the memory location that holds data. It is temporary storage.

Syntax:

 
  1. $variableName=value;

What is the difference between "echo" and "print" in PHP?

Echo can output one or more string but print can only output one string and always returns 1.

Echo is faster than print because it does not return any value.

What is "print" in PHP?

PHP print output a string. It is a language construct not a function. So the use of parentheses is not required with the argument list. Unlike echo, it always returns 1.

Syntax:

 
  1. int print ( string $arg)  

What is "echo" in PHP?

PHP echo output one or more string. It is a language construct not a function. So the use of parentheses is not required. But if you want to pass more than one parameter to echo, the use of parentheses is required.

Syntax:

 
  1. void echo ( string $arg1 [, string $... ] ) 

What are the popular frameworks in PHP?

  • CakePHP
  • CodeIgniter
  • Yii 2
  • Symfony
  • Zend Framework etc.

Explain the difference between PHP4 and PHP5.

PHP4 doesn't support oops concept and uses Zend Engine 1.

PHP5 supports oops concept and uses Zend Engine 2.

What is the name of scripting engine in PHP?

The scripting engine that powers PHP is called Zend Engine 2.

Explain the difference b/w static and dynamic websites?

In static websites, content can't be changed after running the script. You can't change anything on the site. It is predefined.

In dynamic websites, content of script can be changed at the run time. Its content is regenerated every time a user visit or reload. Google, yahoo and every search engine is the example of dynamic website.

What does $GLOBALS mean?

$GLOBALS is associative array including references to all variables which are currently defined in the global scope of the script.

What is the difference between session_unregister() and session_unset()?

The session_unregister() function unregister a global variable from the current session and the session_unset() function frees all session variables.

When do sessions end?

Sessions automatically end when the PHP script finishes executing but can be manually ended using the session_write_close().

How can you propagate a session id?

You can propagate a session id via cookies or URL parameters.

How to initiate a session in PHP?

The use of the function session_start() lets us activating a session.

what is the definition of a session?

A session is a logical object enabling us to preserve temporary data across multiple PHP pages.

How can we automatically escape incoming data?

We have to enable the Magic quotes entry in the configuration file of PHP.

How is it possible to remove escape characters from a string?

The stripslashes function enables us to remove the escape characters before apostrophes in a string.

What does the unset() function mean?

The unset() function is dedicated for variable management. It will make a variable undefined.

What does the unlink() function mean?

The unlink() function is dedicated for file system handling. It simply deletes the file given as entry.

What is the difference between mysqli_fetch_object() and mysqli_fetch_array()?

The mysqli_fetch_object() function collects the first single matching record where mysqli_fetch_array() collects all matching records from the table in an array.

How can we display information of a array variable and readable by a human with PHP?

To be able to display a human-readable result we use print_r().

What is the main difference between require() and require_once()?

require(), and require_once() perform the same task except that the second function checks if the PHP script is already included or not before executing it.

What type of operation is needed when passing values through a form or an URL?

If we would like to pass values through a form or an URL, then we need to encode and to decode them using htmlspecialchars() and urlencode().

How can PHP and HTML interact?

It is possible to generate HTML through PHP scripts, and it is possible to pass pieces of information from HTML to PHP.

What is the meaning of a final class and a final method?

'final' is introduced in PHP5. Final class means that this class cannot be extended and a final method cannot be overridden.

Is multiple inheritance supported in PHP?

PHP supports only single inheritance; it means that a class can be extended from only one single class using the keyword 'extends'.

What is the main difference between PHP 4 and PHP 5?

PHP 5 presents many additional OOP (Object Oriented Programming) features.

How can we display the output directly to the browser?

To be able to display the output directly to the browser, we have to use the special tags <?= and ?>.

What is the correct and the most two common way to start and finish a PHP block of code?

The two most common ways to start and finish a PHP script are:

 <?php [   ---  PHP code---- ] ?> and <? [---  PHP code  ---] ?>

How do you execute a PHP script from the command line?

Just use the PHP command line interface (CLI) and specify the file name of the script to be executed as follows:

php script.php

What stand for PHP ?

PHP means-> PHP: Hypertext Preprocessor.

At begining PHP known as "Personal Home Page"

Current Version 7.4 of PHP.

What does PEAR stand for?

PEAR means "PHP Extension and Application Repository". It extends PHP and provides a higher level of programming for web developers.

Which programming language does PHP resemble?

PHP syntax resembles Perl and C.

What is the meaning of a final class and a final method?

'final' is introduced in PHP5. Final class means that this class cannot be extended and a final method cannot be overridden.

List some of the features of PHP7.

  • Scalar type declarations
  • Return type declarations
  • Null coalescing operator (??)
  • Spaceship operator
  • Constant arrays using define()
  • Anonymous classes
  • Closure::call method
  • Group use declaration
  • Generator return expressions
  • Generator delegation
  • Space ship operator

Explain the difference b/w static and dynamic websites?

In static websites, content can't be changed after running the script. You can't change anything on the site. It is predefined.

In dynamic websites, content of script can be changed at the run time. Its content is regenerated every time a user visit or reload. Google, yahoo and every search engine is the example of dynamic website.

what is php?

It is an open source server-side scripting language which is widely used for web development. It supports many databases like MySQL, Oracle, Sybase, Solid, PostgreSQL, generic ODBC etc. PHP stands for PHP: Hypertext Pre-processor, that earlier stood for Personal Home Pages. Rasmus Lerdorf known as the father of PHP.