PHP INTERVIEW QUESTIONS 70-80

71. What type of inheritance that PHP supports?

PHP Supports single inheritance.

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

Using LIMIT

Using INDEX

Using PRIMARY KEY

73. The structure of table view buyers is as follows:

+----------------+-------------+------+-----+---------+----------------+

| Field | Type | Null | Key | Default | Extra |

+----------------+-------------+------+-----+---------+----------------+

| user_pri_id | int(15) | | PRI | NULL | auto_increment |

| userid | varchar(10) | YES | | NULL | |

+----------------+-------------+------+-----+---------+----------------+

the value of user_pri_id the last row 2345 then What will happen in the following conditions?

Condition1: Delete all the rows and insert another row then. What is the starting value for this auto incremented field user_pri_id ,

Condition2: Delete the last row(having the field value 2345) and insert another row then. What is the value for this auto incremented field user_pri_id

Answer:

Condition1: 2346

Condition2:2346

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

Advantages:php
- Open Source, readily available (you can be using it today) and dual-
licensed - if you are doing non-profit work or not licensing, there is no cost.
- Very Easy to understand Syntax, some really cool features (arrays
are something else!)
- Interfaces very easily with Apache/MySQL
- Server side (no need to futz with client installs - only with
rendering issues if you use CSS).
- Lots of good source code out there to use and/or learn from, as well
as many useful libraries for working with PDFs, graphics, etc.
- Lots of good books and on-line help (php.net is great)
- Platform agnostic, can run on Windows Linux or Mac servers. Also
very scalable.
- Lots of hosting services have it ready to use, no special
configuration (except if you have special security needs)
- Pretty easy to access other web-based tools through PHP (i.e. google
maps, etc.)

Disadvantages of php
- If you want to do more than just HTML/CSS pages on the client you
need to also add javascript, java or other client-side language in
your output (goes for Perl and some other languages).
- The way browsers work make handling data and coding programs more
interesting (technically each page is a new run on the system, so you
have to manage your variables coming in and going out and between
pages. Not hard, just different.)
- Web programming (regardless of language) is open to security flaws
due to unimplemented or unknown vulnerabilities, takes a bit more
caution.

Advantages of MySQL Indexes

Generally speaking, MySQL indexing into database gives you three advantages:

Query optimization: Indexes make search queries much faster.

Uniqueness: Indexes like primary key index and unique index help to avoid duplicate row data.

Text searching: Full-text indexes in MySQL version 3.23.23, users have the opportunity to optimize searching against even large amounts of text located in any field indexed as such.

Disadvantages of MySQL indexes

When an index is created on the column(s), MySQL also creates a separate file that is sorted, and contains only the field(s) you're interested in sorting on.

Firstly, the indexes take up disk space. Usually the space usage isn’t significant, but because of creating index on every column in every possible combination, the index file would grow much more quickly than the data file. In the case when a table is of large table size, the index file could reach the operating system’s maximum file size.

Secondly, the indexes slow down the speed of writing queries, such as INSERT, UPDATE and DELETE. Because MySQL has to internally maintain the “pointers” to the inserted rows in the actual data file, so there is a performance price to pay in case of above said writing queries because every time a record is changed, the indexes must be updated. However, you may be able to write your queries in such a way that do not cause the very noticeable performance degradation

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

The ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set by a specified column.

GROUP BY

The GROUP BY statement is used in conjunction with the aggregate functions to group the result-set by one or more columns.

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

CHAR

CHAR should be used for storing fix length character strings. String values will be space/blank padded before stored on disk. If this type is used to store varibale length strings, it will waste a lot of disk space.

VARCHAR

Currently VARCHAR behaves exactly the same as VARCHAR2. However, this type should not be used as it is reserved for future usage.

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

With the md5 function you can encrypt your text with 32 character hexadecimal number.
For Ex. $str = 'apple'; echo md5($str);
this prints '1f3870be274f6c49b3e31a0c6728957f' 

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

Mysql > LOAD DATA LOCAL INFILE '/path/pet.txt' INTO TABLE pet; 

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

    DATEDIFF(firstdate,seconddate)

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

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