PHP interview Questions 3

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

describe table_name;

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

3 tables will create when we create table. They are
The '.frm' file stores the table definition.
The data file has a '.MYD' (MYData) extension.
The index file has a '.MYI' (MYIndex) extension,

63. What is the purpose of the following files having extensions 1) frm 2) MYD 3) MYI. What these files contains?

In MySql, the default table type is MyISAM.
Each MyISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type.
The '.frm' file stores the table definition.
The data file has a '.MYD' (MYData) extension.
The index file has a '.MYI' (MYIndex) extension,

64. What is maximum size of a database in mysql?

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 Limit
Linux 2.2-Intel 32-bit 2GB (LFS: 4GB)
Linux 2.4+ (using ext3 filesystem) 4TB
Solaris 9/10 16TB
NetWare w/NSS filesystem 8TB
Win32 w/ FAT/FAT32 2GB/4GB
Win32 w/ NTFS 2TB (possibly larger)
MacOS X w/ HFS+ 2TB

65. Give the syntax of Grant and Revoke commands?
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 user

The 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

66. Explain Normalization concept?

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 Form

The 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 Form

Where the First Normal Form deals with redundancy of data across a horizontal row, Second Normal Form (or 2NF) deals with redundancy of data in vertical columns. As stated earlier, the normal forms are progressive, so to achieve Second Normal Form, your tables must already be in First Normal Form.

Third Normal Form

I have a confession to make; I do not often use Third Normal Form. In Third Normal Form we are looking for data in our tables that is not fully dependant on the primary key, but dependant on another value in the table

67. How can we find the number of rows in a table using mysql?

Answer: Use this for mysql
>SELECT COUNT(*) FROM table_name;
but if u r particular about no of rows with some special result
do this
>SELECT [colms],COUNT(*) FROM table_name [where u put conditions];

68. How can we find the number of rows in a result set using php?

Answer: for PHP

$result = mysql_query($any_valid_sql, $database_link);
$num_rows = mysql_num_rows($result);
echo "$num_rows rows found";

69. How many ways we can we find the current date using mysql?

SELECT CURDATE();
CURRENT_DATE() = CURDATE()
for time use
SELECT CURTIME();
CURRENT_TIME() = CURTIME()

70. What are the advantages and disadvantages of CASCADE STYLE SHEETS?

External Style Sheets

Advantages

Can control styles for multiple documents at once
Classes can be created for use on multiple HTML element types in many documents
Selector and grouping methods can be used to apply styles under complex contexts

Disadvantages

An extra download is required to import style information for each document
The rendering of the document may be delayed until the external style sheet is loaded
Becomes slightly unwieldy for small quantities of style definitions

Embedded Style Sheets

Advantages

Classes can be created for use on multiple tag types in the document
Selector and grouping methods can be used to apply styles under complex contexts
No additional downloads necessary to receive style information

Disadvantages

This method can not control styles for multiple documents at once

Inline Styles

Advantages

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

Disadvantages

Does not distance style information from content (a main goal of SGML/HTML)
Can not control styles for multiple documents at once
Author can not create or control classes of elements to control multiple element types within the document
Selector grouping methods can not be used to create complex element addressing scenarios

71. What type of inheritance that php supports? Answer: In PHP an extended class is always dependent on a single base class, that is, multiple inheritance is not supported. Classes are extended using the keyword 'extends'.

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

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

In general, when you want to make a slow SELECT … WHERE query faster, the first thing to check is whether you can add an index. All references between different tables should usually be done with indexes. You can use the EXPLAIN statement to determine which indexes are used for a SELECT. See section 7.4.5 How MySQL Uses Indexes and section 7.2.1 EXPLAIN Syntax (Get Information About a SELECT).
Some general tips for speeding up queries on MyISAM tables:

To help MySQL optimize queries better, use ANALYZE TABLE or run myisamchk –analyze on a table after it has been loaded with data. This updates a value for each index part that indicates the average number of rows that have the same value. (For unique indexes, this is always 1.) MySQL will use this to decide which index to choose when you join two tables based on a non-constant expression. You can check the result from the table analysis by using SHOW INDEX FROM tbl_name and examining the Cardinality value. myisamchk –description –verbose shows index distribution information.

To sort an index and data according to an index, use myisamchk –sort-index –sort-records=1 (if you want to sort on index 1). This is a good way to make queries faster if you have a unique index from which you want to read all records in order according to the index. Note that the first time you sort a large table this way, it may take a long time.

In both cases let the value for auto increment field be n then next row will have value n+1 i.e. 2346

73. What are the advantages/disadvantages of mysql and php?

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

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

To sort a result, use an ORDER BY clause.

The most general way to satisfy a GROUP BY clause is to scan the whole table and create a new temporary table where all rows from each group are consecutive, and then use this temporary table to discover groups and apply aggregate functions (if any).
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

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

char(M) M bytes 0

80. How can we change the name of a column of a table?

MySQL query to rename table: RENAME TABLE tbl_name TO new_tbl_name
[, tbl_name2 TO new_tbl_name2] …
or,
ALTER TABLE tableName CHANGE OldName newName.

81. How can we change the name and data type of a column of a table?

ALTER [IGNORE] TABLE tbl_name
alter_specification [, alter_specification] | CHANGE [COLUMN] old_col_name column_definition
[FIRST|AFTER col_name]

82. What are the differences between drop a table and truncate a table?
Answer: Delete a Table or DatabaseTo delete a table (the table structure, attributes, and indexes will also be deleted).
What if we only want to get rid of the data inside a table, and not the table itself? Use the TRUNCATE TABLE command (deletes only the data inside the table).

83. When you want to show some part of a text displayed on an HTML page in red font color, what different possibilities are there to do this? What are the advantages/disadvantages of these methods?

Using Html font color tag:
I am Amin
Using tag in CSS:
STRONG {color:red}
So when we use the tag:
I am Amin about this.
Using Class in CSS:

.colorclass
{
color:#FF3399;
font-weight:900;
}

I am Amin
If we use html the modification will be trouble some because we have to change the code of the page. But when we use CSS then it will be easy to change the CSS file and we can get the desired out put.

84. When viewing an HTML page in a Browser, the Browser often keeps this page in its cache. What can be possible advantages/disadvantages of page caching? How can you prevent caching of a certain page (please give several alternate solutions)?

When you use the metatag in the header section at the beginning of an HTML Web page, the Web page may still be cached in the Temporary Internet Files folder.

A page that Internet Explorer is browsing is not cached until half of the 64 KB buffer is filled. Usually, metatags are inserted in the header section of an HTML document, which appears at the beginning of the document. When the HTML code is parsed, it is read from top to bottom. When the metatag is read, Internet Explorer looks for the existence of the page in cache at that exact moment. If it is there, it is removed. To properly prevent the Web page from appearing in the cache, place another header section at the end of the HTML ocument. For example:

85. What are the different methods of passing data or information between two calls of a web page? What are the advantages/disadvantages of these methods?

86. An Apache web server is running on a Linux system. Suddenly, the web server delivers the pages very slow. How could you find out possible reasons for that (when using system commands, please specify their names)?

87. What are the different ways to login to a remote server? Explain the means, advantages and disadvantages?

There is at least 3 ways to logon to a remote server:
Use ssh or telnet if you concern with security
You can also use rlogin to logon to a remote server.

88. Please give a regular _expression (preferably Perl/PREG style), which can be used to identify the URL from within a HTML link tag. Example: The regular _expression should match the tag mysqldump -u user -ppassword –opt -full database_name > backupfile.sql
Then move the resulting file(s) to your preferred backup areas. If you require more information on the mysqldump command, then simply check out this URL:www.mysql.com/documentation/mysql
Copy all the relevant table files.

If the server isn't updating anything (or you've deliberately killed mysqld for this purpose) then you can copy all the files with the following extensions in your MySQL data directory:
*.frm
*.myd
*.myi
Make sure you restart the MySQL daemon once you finish copying and downloading the files to your preferred backup areas.
TIP: once you've completed the backup, restart MySQL with the –log-update switch. This will allow you to keep track of all modifications done in the MySQL tables since your last 'dump'.
To restore your dumps, you should either restore to an existing database or create a new database using
shell> mysqladmin create database_name
then issue the following command :
shell> mysql -u user -ppassword database_name