PHP Interview Questions-Answers Part-III

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

Questions : 52 How can I retrieve values from one database server and store them in other database server using PHP?
Answer : 52 we can always fetch from one database and rewrite to another. here is a nice solution of it.

$db1 = mysql_connect("host","user","pwd");
mysql_select_db("db1", $db1);
$res1 = mysql_query("query",$db1);
$db2 = mysql_connect("host","user","pwd");
mysql_select_db("db2", $db2);
$res2 = mysql_query("query",$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

$res3 = mysql_query("query",$db1); //this will failSo how to solve that?

take a look below.

$db1 = mysql_connect("host","user","pwd")
mysql_select_db("db1", $db1);
$res1 = mysql_query("query",$db1);

$db2 = mysql_connect("host","user","pwd", true)
mysql_select_db("db2", $db2);
$res2 = mysql_query("query",$db2);

So mysql_connect 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);

Questions : 53 List out the predefined classes in PHP?
Answer : 53 Directory
stdClass
__PHP_Incomplete_Class
exception
php_user_filter

Questions : 54 How can I make a script that can be bi-language (supports English, German)?
Answer : 54 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.

Questions : 55 What are the difference between abstract class and interface?
Answer : 55 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.

Questions : 56 How can we send mail using JavaScript?
Answer : 56 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.

Questions : 57 How can we repair a MySQL table?
Answer : 57 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

Questions : 58 What are the advantages of stored procedures, triggers, indexes?
Answer : 58 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.

Questions : 59 What is the maximum length of a table name, database name, and fieldname in MySQL?
Answer : 59 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:

Questions : 60 How many values can the SET function of MySQL take?
Answer : 60 MySQL set can take zero or more values but at the maximum it can take 64 values

Questions : 61 What are the other commands to know the structure of table using MySQL commands except explain command?
Answer : 61 describe Table-Name;

Questions : 62 How many tables will create when we create table, what are they?
Answer : 62 The ‘.frm’ file stores the table definition.
The data file has a ‘.MYD’ (MYData) extension.
The index file has a ‘.MYI’ (MYIndex) extension,

Questions : 63 What is the purpose of the following files having extensions 1) .frm 2) .myd 3) .myi? What do these files contain?
Answer : 63 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,

Questions : 64 What is maximum size of a database in MySQL?
Answer : 64 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

Questions : 65 Give the syntax of Grant and Revoke commands?
Answer : 65 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

Questions : 66 Explain Normalization concept?
Answer : 66 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

Questions : 67 How can we find the number of rows in a table using MySQL?
Answer : 67 Use this for mysql

>SELECT COUNT(*) FROM table_name;

Questions : 68 How can we find the number of rows in a result set using PHP?
Answer : 68

$result = mysql_query($sql, $db_link);
$num_rows = mysql_num_rows($result);
echo "$num_rows rows found";

Questions : 69 How many ways we can we find the current date using MySQL?
Answer : 69

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

Questions : 70 What are the advantages and disadvantages of Cascading Style Sheets?
Answer : 70 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 contextsDisadvantagesAn 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

Questions : 71 What type of inheritance that PHP supports?
Answer : 71 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’.

Questions : 72 What is the difference between Primary Key and Unique key?
Answer : 72 Primary Key: A column in a table whose values uniquely identify the rows in the table. A primary key value cannot be NULL.
Unique Key: Unique Keys are used to uniquely identify each row in the table. There can be one and only one row for each unique key value. So
NULL can be a unique key.There can be only one primary key for a table but there can be more than one unique for a table.

Question : 73 what is garbage collection? default time ? refresh time?
Answer : 73 Garbage Collection is an automated part of PHP , If the Garbage Collection process runs, it then analyzes any files in the /tmp for any session files that have not been accessed in a certain amount of time and physically deletes them. Garbage Collection process only runs in the default session save directory, which is /tmp. If you opt to save your sessions in a different directory, the Garbage Collection process will ignore it. the Garbage Collection process does not differentiate between which sessions belong to whom when run. This is especially important note on shared web servers. If the process is run, it deletes ALL files that have not been accessed in the directory. There are 3 PHP.ini variables, which deal with the garbage collector: PHP ini value name default session.gc_maxlifetime 1440 seconds or 24 minutes session.gc_probability 1 session.gc_divisor 100

Questions : 74 What are the advantages/disadvantages of MySQL and PHP?
Answer : 74 Both of them are open source software (so free of cost), support cross platform. php is faster then ASP and JSP.

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

Part-IV Coming soon …



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