ATOS Most Frequently Asked Latest MySQL Interview Questions Answers

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 1 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

ATOS Most Frequently Asked Latest MySQL Interview Questions Answers

How Do You Determine The Location Of Mysql Data Directory?

The default location of MySQL data directory in windows is C:mysqldata or C:Program FilesMySQLMySQL Server 5.0 data.

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 data directory.

What Is The Use Of Mysql_close()?

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

How Is 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

What Is The Usage Of Enums In Mysql?

ENUMs are used to limit the possible values that go in the table:

For example: CREATE TABLE months (month ENUM 'January', 'February', 'March'); INSERT months VALUES ('April').

What are ENUMs used for in MySQL?

ENUM is used to limit the possible values and store it together. It is a function that can be created to store the similar values together. It is used in creation of table.

The syntax of it is as follows:

CREATE TABLE months (month ENUM “January”, “February”, “March”,…);
INSERT months VALUES (“April”);

What is the purpose of -> in the MySQL terminal?

-> prompt in the command of MySQL indicates that a single statement is being entered across multiple lines. From this prompt MySQL interprets that you haven’t finished entering the statements. It has no impact of enter which you might press to go to the next line. MySQL will execute the statement only when you will insert the semicolon in the end which it recognizes.

How to find the unique values if the value in the column is repeated?

If the values in the column of a table are repeating and a unique value has to be found then the following command can be used in the query:

SELECT DISTINCT user_firstname FROM users;

There is another command which can be used to find the command to see the distinct values as:

SELECT COUNT (DISTINCT user_firstname) FROM users;

When to use ORDER BY in DELETE statement?

The ORDER BY clause in DELETE statement is used when a deletion has to take place by in a specified order.

The syntax is like this

DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]
ORDER BY

clause is specified, the rows are deleted in the order that is specified.

What is the difference between Unix timestamps and MySQL timestamps?

The unix timestamp is stored as 32 bit integer whereas, MySQL timestamps are stored in 32 bit integers but represented differently then UNIX timestamps like YYYY-MM-DD HH:MM:SS format. Unix timestamp is given as month-day-year-HH:MM:SS..

Why Do We Use Mysql Database Server?

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 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

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 $result is the result resource returned from a successful query executed using the mysql_query() function.
Example:
1.$result = mysql_query("SELECT * from students");
2.while($row = mysql_fetch_row($result))
3.{
4.Some statement;
5.}

How Do You Backup A Database In Mysql?

It is easy to backing up data with phpMyAdmin. Select the database you want to backup by clicking the database name in the left hand navigation bar. Then click the export button and make sure that all tables are highlighted that you want to backup. Then specify the option you want under export and save the output.

What Is Sqlyog?

SQLyog program is the most popular GUI tool for admin. It is the most popular MySQL manager and admin tool. It combines the features of MySQL administrator, phpMyadmin and others MySQL front ends and MySQL GUI tools.

What Is The Difference Between Char And Varchar?

A list of differences between CHAR and VARCHAR:

CHAR and VARCHAR types are different in storage and retrieval.
CHAR column length is fixed to the length that is declared while creating table. The length value ranges from 1 and 255.
When CHAR values are stored then they are right padded using spaces to specific length. Trailing spaces are removed when CHAR values are retrieved.

What Is The Difference Between Truncate And Delete In Mysql?

The DELETE command is used to delete data from a table. It only deletes the rows of data from the table while, truncate is very dangerous command and should be used carefully because it deletes every row permanently from a table.

How Many Triggers Are Possible In Mysql?

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

Before Insert
After Insert
Before Update
After Update
Before Delete
After Delete

How to display top 50 rows?

In MySql, top 50 rows are displayed by using this following query:


SELECT * FROM
LIMIT 0,50;
1
2
SELECT * FROM
LIMIT 0,50;