Mysql interview questions

Friday, 31 January 2020

40+ Approved .edu and .gov backlinks for your websites

Hello, friends today I am going to share 40.gov and .edu backlinks for your website so you can rank faster on Google. These backlinks definitely help you to increase your domain DA and PA.

Tips to Improve Website & Blog Content Visibility

After adding an optimized page to your website or post to your blog, Google and other search engines will "index" it. After that, it will be found in the organic search results.

You can improve your content visibility and SEO by doing things outside of your website/blog. The tips below are a good starting point for promoting your website and its content.

Social Media

Set up social media profiles that make sense for your business:
Facebook page and profile
LinkedIn profiles and groups
Twitter account
Pinterest or Instagram for photos
Post to each social media and link to content when something is new (blog post, sale) or you have an announcement.
Start conversations to share ideas.
Use a social media management tool like HootSuite.
Add more flexible social media sharing to your blog posts.

Social Bookmarking websites

Use social bookmarking to share links to your posts and pages. Here are some popular sites:

Twitter
StumbleUpon
Dribble
Pocket
Digg
Slashdot
We Heart It
scoop.it

Get comments on your own blog and participate in the conversation

To get the conversation going, ask people (friends/customers) to comment
Ask a question at the end of blog posts to entice people to share thoughts on a topic
Reply when people comment
Always moderate comments to eliminate spam from automatically showing on your blog

Participate in Forums and Comment on blogs in your niche

Leave meaningful comments that add to the conversation or ask questions.
Set up profiles with a link back to your blog.
Look into using a Disqus.com profile.
Join industry or local organizations

Choose organizations that relate to your web/blog content:

Better Business Bureau
Chamber of Commerce
Industry Associations
Create profiles that link back to your blog and website.

Please share any content promotion tips that you find useful by leaving a comment below. Thanks!

Tuesday, 7 November 2017

Write command to import an mysql file

Run below command on terminal to import a mysql database from file

mysql -u username -p database_name < file.sql

How to get a list of MySQL user accounts

To get the list of MySQL user accounts run below query:

SELECT User FROM mysql.user;

Monday, 24 July 2017

How to delete records from multiple tables in MYSQL with one query

Delete records from multiple tables with one query.

CREATE TABLE table_a (
  id INT(11) DEFAULT NULL
);

CREATE TABLE table_b (
  id INT(11) DEFAULT NULL
);

INSERT INTO table_a VALUES 
  (2),
  (3),
  (1);

INSERT INTO table_b VALUES 
  (2),
  (5),
  (1);

Delete records:

DELETE t1, t2
FROM
  table_a t1
JOIN table_b t2
  ON t1.id = t2.id
WHERE
  t1.id = 1;

Check results:

SELECT * FROM table_a;
+------+
| id   |
+------+
|    2 |
|    3 |
+------+

SELECT * FROM table_b;
+------+
| id   |
+------+
|    2 |
|    5 |
+------+

How to copy records from one table too another in Mysql ?

In this example we are going to see the mysql query to copy data from one table too another.

 
INSERT INTO table_b SELECT id, column_a FROM table_a;

What is the DELIMITER in MySQL and what it’s used for?

The DELIMITER command is used to change the standard delimiter of MySQL commands. The standard command delimiter is the ';' character that defines the end of the query.

Example:

INSERT INTO actor VALUES (1, 'PENELOPE', 'GUINESS', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (2, 'NICK', 'WAHLBERG', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (3, 'ED', 'CHASE', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (4, 'JENNIFER', 'DAVIS', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (5, 'JOHNNY', 'LOLLOBRIGIDA', '2006-02-15 04:34:33');

Now let’s have a look at the following script. It consists of several INSERT queries, procedure creating and several more INSERT queries.

INSERT INTO actor VALUES (6, 'BETTE', 'NICHOLSON', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (7, 'GRACE', 'MOSTEL', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (8, 'MATTHEW', 'JOHANSSON', '2006-02-15 04:34:33');
CREATE PROCEDURE find_actors(IN actor_list VARCHAR(255))
BEGIN
  SET @select = CONCAT('SELECT * FROM actor WHERE actor_id IN (', actor_list, ')');
  PREPARE stmt FROM @select;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END;
INSERT INTO actor VALUES (9, 'JOE', 'SWANK', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (10, 'CHRISTIAN', 'GABLE', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (11, 'ZERO', 'CAGE', '2006-02-15 04:34:33');

When executing a script, MySQL client parses queries by delimiting them by ';' and sends them to a server.

If we execute the script in whole, we get the syntax error - 'ERROR 1064 (42000): You have an error in your SQL syntax;...'. This is because the MySQL client has extracted the following command and tried to execute it.


CREATE PROCEDURE find_actors(IN actor_list VARCHAR(255))
BEGIN
SET @select = CONCAT('SELECT * FROM actor WHERE actor_id IN (', actor_list, ')');

The point is that some objects in MySQL may contain executable code in the BEGIN...END clause and commands in the code are delimited by the ';' character; such objects may include: stored procedures and functions, triggers, and events.

In this case, somehow we have to extract the create procedure command in whole. There is the DELIMITER client side command that allows you to set its conditional query delimiter. Any character or string can be set as a delimiter. The most common are $$ and //. In our example the ‘$$’ string is used.

Below is the script with using the DELIMITER command -

INSERT INTO actor VALUES (6, 'BETTE', 'NICHOLSON', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (7, 'GRACE', 'MOSTEL', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (8, 'MATTHEW', 'JOHANSSON', '2006-02-15 04:34:33');
-- Set new delimiter '$$'
DELIMITER $$
CREATE PROCEDURE find_actors(IN actor_list VARCHAR(255))
BEGIN
  SET @select = CONCAT('SELECT * FROM actor WHERE actor_id IN (', actor_list, ')');
  PREPARE stmt FROM @select;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END
$$ -- End of command
-- Set default delimiter ';'
DELIMITER ;
INSERT INTO actor VALUES (9, 'JOE', 'SWANK', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (10, 'CHRISTIAN', 'GABLE', '2006-02-15 04:34:33');
INSERT INTO actor VALUES (11, 'ZERO', 'CAGE', '2006-02-15 04:34:33');

Now our script will be executed with no errors and the create procedure command will succeed. It's also important to note that the DELIMITER command may be set only once for the whole set of commands.

The example -

-- Set new delimiter '$$'
DELIMITER $$
CREATE PROCEDURE find_actors(IN actor_list VARCHAR(255))
BEGIN
  SET @select = CONCAT('SELECT * FROM actor WHERE actor_id IN (', actor_list, ')');
  PREPARE stmt FROM @select;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END
$$ -- End of command
CREATE FUNCTION inventory_held_by_customer(p_inventory_id INT)
  RETURNS INT(11)
  READS SQL DATA
BEGIN
  DECLARE v_customer_id INT;
  DECLARE EXIT HANDLER FOR NOT FOUND RETURN NULL;
  SELECT customer_id INTO v_customer_id FROM rental
    WHERE return_date IS NULL AND inventory_id = p_inventory_id;
  RETURN v_customer_id;
END
$$ -- End of command
CREATE TRIGGER ins_film
  AFTER INSERT
  ON film
  FOR EACH ROW
BEGIN
  INSERT INTO film_text (film_id, title, description) VALUES (NEW.film_id, NEW.title, NEW.description);
END
$$ -- End of command
-- Set default delimiter ';'
DELIMITER ;

Source: http://buysql.com/mysql/42-delimiter-mysql.html

Tuning performance of MySQL Server Database

MySQL can be a rock solid, lighting quickly database server which has been designed for two factors pace and efficiency. It could be the Ferrari of databases: Light weight, quickly and Built for the higher pace tracks! I nonetheless hear an awful lot of stories from owners whose databases are running too slow. In my experience, the three principal places to seem for issues are:

Faulty Database Design
Lousy Queries
Server factors

Faulty Database Design

Correct database design might be the single most essential factor for the ensuring efficiency and maintainability with the database. Right here is what you have to answer when designing a desk: Can I decrease the size of knowledge that every row will have? Right here is what you are able to do:

Use unsigned numeric values when the application is not going to save negative numbers. Like the quantity ordered of an item in an e-commerce application is never going to become -$125.
Use Variable length values as an alternative to fixed length worth i.e. utilized varchar in place of char.
Tend not to use unnecessarily big field sizes. For most e-commerce application unsigned small int is extra than sufficient to retailer inventory count. A field described as unsigned small int can keep a max benefit of 65535.
Don't ignore normalization; its helps prevent unnecessary repetition of info. The part B of that is, don't overuse normalization. If the desk is not going to grow in size substantially, there's no point in normalization. For instance, if the user desk has just 20 rows (i.e. 20 employees in an organization), all attempts of normalization are wasted.
Use Keys. Don't decide keys by The customer id has to become indexed from the order desk. If the order desk is becoming searched 90% of your times by order date, it makes much more sense to index order date.

Remember, how a desk will probably be employed must determine how it truly is designed. Spending time right here will save years of frustration.

Lousy Queries

It sounds too excellent to become true but you won't believe the number of developers out there who totally suck at writing queries. You will discover two kinds of undesirable queries:

Unnecessary Queries: These are the queries that shouldn't have been made inside initial place. The only method to avoid it can be asking, Do I actually need to have this info?
Inefficient Queries: These are the queries that usually do not use the underlying disk structure or MySQL functions inside correct way.

Right here is actually a starting point to begin looking at issue areas:

Unnecessary utilization of Select * statements when the entire processing is becoming carried out on a single column. The far more info is fetched from the server the extra work MySQL has to do and much more bandwidth it takes.
Employing sub-query as an alternative to a join. On a correctly designed database, joins are incredibly rapidly. Making use of sub-queries just shows a lack of knowledge.
Improper use of Keys. It can be especially valid for range checks. Remember to use the Explain statement to check the utilization of keys and then use the use crucial statement in your where clauses to force critical utilization.

Server Factors

Every thing carried out correctly, there nonetheless may well be some server factors that may possibly be causing the technique to become slow. These are:

Hardware associated
Server configuration associated

Right here is what you are able to do about the hardware:

The extra RAM is the method the much better it can be. MySQL often fetches info from the RAM and a lot more the RAM is on the technique, the much better it can be.
Purchase the fastest achievable RAM! A slower RAM is just irony.
As soon as you will be settled with the RAM size and velocity, seem for processing velocity. MySQL can use multiple processors.

As soon as you might be satisfied with the hardware, you will find a set of variables in my.cnf that you should seem at:

key_buffer_size: This describes the memory accessible to save the index keys. The default is 8 MB but you may set it to 25% with the RAM.
query_cache_size: This worth is by default ..! if you might have a great deal of repeating queries like in reporting applications and so on, make certain you set this benefit largely.
table_open_cache: This determines the number of desk descriptors that MySQL will maintain inside the cache. The default worth is 64. But, if you've 100 users accessing a disk concurrently then this worth require to at-least be 100. You also need to take into considerations joins and so on.

Source: http://www.articlesfactory.com/articles/computers/improving-mysql-server-database-performance.html

Friday, 31 January 2020

40+ Approved .edu and .gov backlinks for your websites

Tips to Improve Website & Blog Content Visibility

Social Media

Social Bookmarking websites

Tuesday, 7 November 2017

Write command to import an mysql file

How to get a list of MySQL user accounts

Monday, 24 July 2017

How to delete records from multiple tables in MYSQL with one query

How to copy records from one table too another in Mysql ?

What is the DELIMITER in MySQL and what it’s used for?

Tuning performance of MySQL Server Database

Faulty Database Design

Lousy Queries

Server Factors

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