November 1, 2018

Sreekanth B

Hewlett-Packard MySQL Most Frequently Asked Latest Interview Questions Answers

How To Rename An Existing Column In A Table?

ALTER TABLE tip CHANGE COLUMN subject title VARCHAR(60);

How To Rename An Existing Table In Mysql?

ALTER TABLE tip RENAME TO faq;

How To Create A Table Index In Mvsql?

If you have a table with a lots of rows, and you know that one of the columns will be used often as a search criteria, you can add an index for that column to improve the search performance. To add an index, you can use the “CREATE INDEX” statement as shown in the following script:

<pre>mysql> CREATE TABLE tip (id INTEGER PRIMARY KEY,
subject VARCHAR(80) NOT NULL,
description VARCHAR(256) NOT NULL,
create_date DATE NULL);  Query OK,
0 rows affected (0.08 sec)</pre>
mysql> CREATE INDEX tip_subject ON tip(subject);
Query OK,
0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

How To Get A List Of Indexes Of An Existing Table?

If you want to see the index you have just created for an existing table, you can use the “SHOW INDEX FROM tableName” command to get a list of all indexes in a given table.
Hewlett-Packard MySQL Most Frequently Asked Latest Interview Questions Answers
Hewlett-Packard MySQL Most Frequently Asked Latest Interview Questions Answers

How To Drop An Existing Index In Mysql?

If you don’t need an existing index any more, you should delete it with the “DROP INDEX indexName ON tableName” statement. Here is an example SQL script :

mysqi> DROP INDEX tip_subject ON tip;
Query OK, 0 rows affected (0.13 sec)
Records: 0 Duplicates: 0 Warnings: 0

How To Drop An Existing View In Mysql?

If you have an existing view, and you dont want it anymore, you can delete it by using the “DROP VIEW viewName” statement

How To Create A New View In Mysql?

You can create a new view based on one or more existing tables by using the

“CREATE VIEW viewName AS selectStatement” .

How To Increment Dates By 1111 Mysql?

If you have a date, and you want to increment it by 1 day, you can use the DATE_ADD(date, INTERVAL 1 DAY) function. You can also use the date interval add operation as “date + INTERVAL 1 DAY.

Differentiate between FLOAT and DOUBLE?

Following are differences for FLOAT and DOUBLE:

• Floating point numbers are stored in FLOAT with eight place accuracy and it has four bytes.


• Floating point numbers are stored in DOUBLE with accuracy of 18 places and it has eight bytes.

 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.

How to represent ENUMs and SETs internally?

ENUMs and SETs are used to represent powers of two because of storage optimizations.

What is the usage of ENUMs in MySQL?

ENUM is a string object used to specify set of predefined values and that can be used during table creation.


Create table size(name ENUM('Small', 'Medium','Large');
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Create table size(name ENUM('Small', 'Medium','Large');

Define REGEXP?

REGEXP is a pattern match in which  matches pattern anywhere in the search value.

Difference between CHAR and VARCHAR?

Following are the differences between CHAR and VARCHAR:

CHAR and VARCHAR types differ 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 are the technical features of MySQL?

MySQL database software is a client or server system which includes

Multithreaded SQL server supporting various client programs and libraries
Different backend
Wide range of application programming interfaces and
Administrative tools.

Why MySQL is used?

MySQL database server is reliable, fast and very easy to use.  This software can be downloaded as freeware and can be downloaded from the internet.

What are Heap tables?

HEAP tables are present in memory and they are used for high speed storage on temporary

basis.

• BLOB or TEXT fields are not allowed

• Only comparison operators can be used =, <,>, = >,=<

• AUTO_INCREMENT is not supported by HEAP tables

• Indexes should be NOT NULL

What is the default port for MySQL Server?

The default port for MySQL server is 3306.

What are the advantages of MySQL when compared with Oracle?

MySQL is open source software which is available at any time and has no cost involved.
MySQL is portable
GUI with command prompt.
Administration is supported using MySQL Query Browser

Give string types available for column?

The string types are:

SET
BLOB
ENUM
CHAR
TEXT
VARCHAR

How to get current MySQL version?

SELECT VERSION ();
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SELECT VERSION ();
is used to get the current version of MySQL.

What storage engines are used in MySQL?

Storage engines are called table types and data is stored in files using various techniques.

Technique involves:

Storage mechanism
Locking levels
Indexing
Capabilities and functions.

What is the difference between MyISAM Static and MyISAM Dynamic?

In MyISAM static all the fields will have fixed width. The Dynamic MyISAM table will have fields like TEXT, BLOB, etc. to accommodate the data types with various lengths.

MyISAM Static would be easier to restore in case of corruption.

What are all the Common SQL Function?

CONCAT(A, B) – Concatenates two string values to create a single string output. Often used to combine two or more fields into one single field.

FORMAT(X, D) – Formats the number X to D significant digits.

CURRDATE(), CURRTIME() – Returns the current date or time.

NOW() – Returns the current date and time as one value.

MONTH(), DAY(), YEAR(), WEEK(), WEEKDAY() – Extracts the given data from a date value.

HOUR(), MINUTE(), SECOND() – Extracts the given data from a time value.

DATEDIFF(A, B) – Determines the difference between two dates and it is commonly used to calculate age

SUBTIMES(A, B) – Determines the difference between two times.

FROMDAYS(INT) – Converts an integer number of days into a date value.

Explain Access Control Lists.

An ACL (Access Control List) is a list of permissions that is associated with an object. This list is the basis for MySQL server’s security model and it helps in troubleshooting problems like users not being able to connect.

MySQL keeps the ACLs (also called grant tables) cached in memory. When a user tries to authenticate or run a command, MySQL checks the authentication information and permissions against the ACLs, in a predetermined order.

What are federated tables?

Federated tables which allow access to the tables located on other databases on other servers.

What, if a table has one column defined as TIMESTAMP?

Timestamp field gets the current timestamp whenever the row gets altered.

What happens when the column is set to AUTO INCREMENT and if you reach maximum value in the table?

It stops incrementing. Any further inserts are going to produce an error, since the key has been used already.

How can we find out which auto increment was assigned on Last insert?

LAST_INSERT_ID will return the last value assigned by Auto_increment and it is not required to specify the table name.

How can you see all indexes defined for a table?

Indexes are defined for the table by:

SHOW INDEX FROM <tablename>;

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