MySQL Interview Questions

You can add a User by using the CREATE command and specifying the necessary credentials. For example:

CREATE USER ‘testuser’ IDENTIFIED BY ‘sample password’;

BLOB is an acronym that stands for a binary large object. It is used to hold a variable amount of data.
There are four types of BLOB:

• TINYBLOB
• BLOB
• MEDIUMBLOB
• LONGBLOB

A BLOB can hold a very large amount of data. For example - documents, images, and even videos. You could store your complete novel as a file in a BLOB if needed.

Example: To select the records with an Order Date of "2018-11-11" from a table:

SELECT * FROM Orders WHERE OrderDate='2018-11-11'

MySQL is a database management system for web servers. It can grow with the website as it is highly scalable. Most of the websites today are powered by MySQL.

MySQL has numeric data types for integer, fixed-point, floating-point, and bit values, as shown in the table below. Numeric types can be signed or unsigned, except BIT. A special attribute enables the automatic generation of sequential integer or floating-point column values, which is useful for applications that require a series of unique identification numbers.

One can view all the databases on the MySQL server host using the following command:

mysql> SHOW DATABASES;  

In MySQL, the DELETE statement is used to delete records from a table:

DELETE FROM table_name
WHERE column_name = value_name

In MySQL, there are different index types, such as a regular INDEX, a PRIMARY KEY, or a FULLTEXT index. You can achieve fast searches with the help of an index. Indexes speed up performance by either ordering the data on disk so it's quicker to find your result or, telling the SQL engine where to go to find your data.

Example: Adding indexes to the history table:

ALTER TABLE history ADD INDEX(author(10));
ALTER TABLE history ADD INDEX(title(10));
ALTER TABLE history ADD INDEX(category(5));
ALTER TABLE history ADD INDEX(year);
DESCRIBE history;

You can remove a column by using the DROP keyword:

ALTER TABLE classics DROP pages;

The INSERT INTO statement is used to add new records to a MySQL table:

INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...)

If we want to add values for all the columns of the table, we do not need to specify the column names in the SQL query. However, the order of the values should be in the same order as the columns in the table. The INSERT INTO syntax would be as follows:

INSERT INTO table_name
VALUES (value1, value2, value3, ...);

Use the following to create a table using MySQL:

CREATE TABLE history (
author VARCHAR(128),
title VARCHAR(128),
type VARCHAR(16),
year CHAR(4)) ENGINE InnoDB;

Use the following command to create a new database called ‘books’:

CREATE DATABASE books;

A query is a specific request or a question. One can query a database for specific information and have a record returned.

There are three main ways you can interact with MySQL: 

• using a command line
• via a web interface
• through a programming language

A MySQL database contains one or more tables, each of which contains records or rows. Within these rows are various columns or fields that contain the data itself.

The SQL in MySQL stands for Structured Query Language. This language is also used in other databases such as Oracle and Microsoft SQL Server.  One can use commands such as the following to send requests from a database:

SELECT title FROM publications WHERE author = ' J. K. Rowling’;

Note that SQL is not case sensitive. However, it is a good practice to write the SQL keywords in CAPS and other names and variables in a small case.

You can check out this SQL Tutorial to learn more about SQL. 

A database is a structured collection of data stored in a computer system and organized in a way to be quickly searched. With databases, information can be rapidly retrieved.

• Flexibility: MySQL runs on all operating systems
• Power: MySQL focuses on performance
• Enterprise-Level SQL Features: MySQL had for some time been lacking in advanced features such as subqueries, views, and stored procedures.
• Full-Text Indexing and Searching
• Query Caching: This helps enhance the speed of MySQL greatly
• Replication: One MySQL server can be duplicated on another, providing numerous advantages
• Configuration and Security

There are three categories of relationships in MySQL:

• One-to-One: Usually, when two items have a one-to-one relationship, you just include them as columns in the same table.
• One-to-Many: One-to-many (or many-to-one) relationships occur when one row in one table is linked to many rows in another table.
• Many-to-Many: In a many-to-many relationship, many rows in one table are linked to many rows in another table. To create this relationship, add a third table containing the same key column from each of the other tables

Several MySQL programs are available to help you communicate with the server. For administrative tasks, some of the most important ones are listed here:

• mysql—An interactive program that enables you to send SQL statements to the server and to view the results. You can also use mysql to execute batch scripts (text files containing SQL statements).

• mysqladmin—An administrative program for performing tasks such as shutting down the server, checking its configuration, or monitoring its status if it appears not to be functioning properly.

• mysqldump—A tool for backing up your databases or copying databases to another server.

• mysqlcheck and myisamchk—Programs that help you perform table checking, analysis, and optimization, as well as repairs if tables become damaged. mysqlcheck works with MyISAM tables and to some extent with tables for other storage engines. myisamchk is for use only with MyISAM tables.

The server, mysqld, is the hub of a MySQL installation; it performs all manipulation of databases and tables.

There are six Triggers allowed to use in the MySQL database:

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

A trigger is a task that executes in response to some predefined database event, such as after a new row is added to a particular table. Specifically, this event involves inserting, modifying, or deleting table data, and the task can occur either prior to or immediately following any such event. 
Triggers have many purposes, including:

• Audit Trails
• Validation
• Referential integrity enforcement

Creating a view is accomplished with the CREATE VIEW statement. As an example:

CREATE
   [OR REPLACE]
   [ALGORITHM = {MERGE | TEMPTABLE | UNDEFINED }]
   [DEFINER = { user | CURRENT_USER }]
   [SQL SECURITY { DEFINER | INVOKER }]
   VIEW view_name [(column_list)]
   AS select_statement
   [WITH [CASCADED | LOCAL] CHECK OPTION]

In MySQL, a view consists of a set of rows that is returned if a particular query is executed. This is also known as a ‘virtual table’. Views make it easy to retrieve the way of making the query available via an alias. 
The advantages of views are:

• Simplicity
• Security
• Maintainability

To be able to use MySQL’s transaction facility, you have to be using MySQL’s InnoDB storage engine (which is the default from version 5.5 onward). If you are not sure which version of MySQL your code will be running on, rather than assuming InnoDB is the default engine you can force its use when creating a table, as follows.

The process of breaking up large tables into smaller chunks (called shards) that are spread across multiple servers is called Sharding. 
The advantage of Sharding is that since the sharded database is generally much smaller than the original; queries, maintenance, and all other tasks are much faster.

In MySQL, scaling capacity is actually the ability to handle the load, and it’s useful to think of load from several different angles such as:

• Quantity of data
• Number of users
• User activity
• Size of related datasets

The top layer contains the services most network-based client/server tools or servers need such as connection handling, authentication, security, and so forth.
The second layer contains much of MySQL’s brains. This has the code for query parsing, analysis, optimization, caching, and all the built-in functions.

The third layer contains the storage engines that are responsible for storing and retrieving the data stored in MySQL.

Several free or low-cost database management systems are available from which to choose, such as MySQL, PostgreSQL, or SQLite.

When you compare MySQL with other database systems, think about what’s most important to you. Performance, features (such as SQL conformance or extensions), support, licensing conditions, and price all are factors to take into account.

MySQL is one of the best RDBMS being used for developing various web-based software applications.

MySQL is offered under two different editions: the open-source MySQL Community Server and the proprietary Enterprise Server.
Given these considerations, MySQL has many attractive qualities:

• Speed
• Ease of use
• Query language support
• Capability
• Connectivity and security
• Portability
• Availability and cost
• Open distribution and source code

Few MySQL References: 

• https://www.mysql.com
• https://learning.oreilly.com/library/view/learning-mysql/0596008643/

Recommended Resources

• Database Testing Interview Questions
• Technical Interview Questions
• PostgreSQL vs MySQL
• SQL Vs MySQL
• MongoDB vs MySQL