Introduction

A MySQL Interview Questions blog discusses the questions with proper explanations. In the era of 2.5 Quintillion bytes of data being generated daily, data plays a crucial role in decision-making for business operations. The Relational Database Management System(RDBMS) is one of the most popular systems available.

This type of DBMS uses a structure that allows the users to identify and access data about another piece of data in the database, and MySQL is one such popular RDBMS. In this article on MySQL Interview Questions, I will be discussing the top questions related to MySQL asked in your interviews.

What is MySQL?

MySQL is an open-source relational database management system (RDBMS). It runs on the web as well as on the server. MySQL is fast, reliable, and easy to use. It is open-source software. MySQL uses standard SQL and compiles on several platforms. It is a multithreaded, multi-user SQL database management system. The data in a MySQL database is stored in the form of tables. A table is a collection of related data consisting of columns and rows.

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MySQL Interview Questions

These MySQL interview questions can be classified majorly into the following three categories:

• Basic MySQL Interview Questions for Freshers
• Intermediate MySQL Interview Questions
• Advanced MySQL Interview Questions 

Basic MySQL Interview Questions

What do you mean by ‘databases’?

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

What is SQL Server?

You must prepare this as it will be asked during MySQL Interview Questions.

SQL Server is one of the database management systems (DBMS) and is designed by Microsoft. DBMS are computer software applications capable of interacting with users, various other applications, and databases. The objective of an SQL Server is capturing and analyzing data and managing the definition, querying, creation, updating, and administration of the database.

What is Database Black Box Testing?

Database Black Box Testing deals with data mapping, data storing and retrieving. Database Black Box Testing is used for Equivalence Partitioning and Boundary Value Analysis techniques. 

How can you Interact with MySQL?

There are three main ways you can interact with MySQL: 

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

What do DDL, DML, and DCL stand for?

DDL is the abbreviation for Data Definition Language dealing with database schemas and describing how data resides in the database. An example of this is the CREATE TABLE command. DML denotes Data Manipulation Language, which includes commands such as SELECT, INSERT, etc. DCL stands for Data Control Language and includes commands like GRANT, REVOKE, etc

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How to create an Index in MySQL?

During MySQL Interview Questions, the interviewer may ask you to explain how you create an Index in MySQL. MySQL has 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 ordering the data on disk so it’s quicker to find your result or telling the SQL engine where to find your data.

What is the Difference Between CHAR and VARCHAR?

When a table is created, CHAR defines the fixed length of the table and columns. The length value could be in the range of 1–255. The VARCHAR command adjusts the column and table lengths as required. So, this is something you must prepare as it will be asked during MySQL Interview Questions

How to Create an Index?

There are different indexes in MySQL, like a regular INDEX, a PRIMARY KEY, or a FULLTEXT index. Indexes are created on a column basis. Indexing helps quickly search for results by ordering the data on disk or telling the SQL engine which location to find your data.

Syntax:

ALTER TABLE history ADD INDEX(author(10));

How do you Add Users in MySQL?

The CREATE command and the necessary credentials can be used to add users.

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

Intermediate MySQL Interview Questions

What are MySQL “Views”?

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

What are MySQL Triggers?

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 before or immediately following any such event. 

Triggers have many purposes, including:

• Audit Trails
• Validation
• Referential integrity enforcement

What are the Types of Relationships Used in MySQL?

During MySQL Interview Questions, the interviewer may ask you about the relationships used in MySQL. There are three categories of relationships in MySQL:

• One-to-One: When two items have a one-to-one relationship, you 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.
• Many-to-Many: In a many-to-many relationship, many rows in one table are linked to many rows in another. MySQL Interview Questions, To create this relationship, add a third table containing the same key column from the other tables.

What are Heap Tables?

Heap tables are in-memory tables used for high-speed temporary storage. But TEXT or BLOB fields are not allowed within them. They also do not support AUTOINCREMENT.

What is the Difference Between a Primary key and a Unique key?

While both are used to enforce the uniqueness of the column defined, the primary key would create a clustered index, whereas the unique key would create a non-clustered index on the column. The primary key does not allow ‘NULL’, but the unique key does

Can you Tell the Difference Between ereg_replace() and eregi_replace()?

ereg_replace and eregi_repalce() are regular expressions used to replace the matching characters. The only difference between these functions is eregi_replace() function ignores the case distinction when it matches alphabetic characters. 

What is a Cursor?

Considered a pointer to point to one row in a set of rows, a Cursor is no thing but a control that enables traversal over the records in the table. So, the cursor performs traversing actions such as adding, retrieving, and removing records in a database. So, this is something you must prepare as it will be asked during MySQL Interview Questions.

How to use the MySQL Slow Query Log?

Information provided on the slow query log could be huge. The query could also be listed over a thousand times. To summarize the slow query log in an informative manner, one can use the third-party tool ‘pt-query-digest’.

Advanced MySQL Interview Questions

Can you explain the logical architecture of MySQL?

During MySQL Interview Questions, the interviewer may ask you to explain the logical architecture of MySQL. The top layer contains the services most network-based client tools or servers need, such as connection handling, authentication, security, etc.

The second layer contains much of MySQL’s brains. This has the coding for query parsing, analysis, optimization, caching, and all the built-in functions.

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

What is Scaling in MySQL?

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

• Quantity of data
• Number of users
• User Activity
• Size of related dataset

What is Sharding in SQL?

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.

What are Transaction Storage Engines in MySQL?

To use MySQL’s transaction facility, you have to use MySQL’s InnoDB storage engine (which is the default from version 5.5 onward). If you are still determining 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. So, this is something you must prepare as it will be asked during MySQL Interview Questions

How can you Validate Emails using a Single Query?

You can use the regular expressions function (REGEXP_LIKE) to validate emails. Consider the below query.

SELECT

Email

FROM

Employee

where NOT REGEXP_LIKE(Email, ‘[A-Z0-9._%+-]+@[A-Z0-9.-]+.[A-Z]{2,4}’, ‘i’);

What is the main Difference Between MySQL and PostgreSQL?

The primary difference between MySQL and PostgreSQL are:

My SQL is purely a relational database, whereas PostgreSQL is an object-relational database. PostgreSQL is more complex and slower than MySQL. In MYSQL, troubleshooting is easy, but challenging to troubleshoot PostgreSQL. MySQL does not support the materialized view, whereas PostgreSQL supports the materialized view.

What are the Types of Joins in MySQL?

There are four types of joins in MySQL. SQL codes, Inner join returns the rows if at least one match exists in two tables. Left join returns all the rows from the left table even if there is no match in the right table. Right, join returns all the rows from the right table even if no conflicts exist in the left table. Full join would return rows when at least one match exists in the tables.

Where is the MyISAM Table Stored?

Every MyISAM Table is stored on disk in the following three files:

• .frm file – Stores the table definition.
• .MYD file – A data file has an MYData extension.
• .MYI index file – The index file has an MYIndex extension

Conclusion

So this brings us to the end of the MySQL Interview Questions blog. This set of MySQL Interview Questions will help you ace your job interview. RDBMS uses a structure that allows the users to identify and access data concerning another piece of data in the database, and MySQL is one such popular RDBMS. In this article on MySQL Interview Questions, I will be discussing the top questions related to MySQL asked in your interviews.

Frequently Asked Questions

1. What is MySQL’s short answer?

 MySQL is one of the most popular open-source DBMS (database management systems). MySQL is easy to use, reliable, and fast—a DB management system that works on embedded and client-server systems.

2. What is the difference between MySQL and SQL?

So, this is something you must prepare as it will be asked during MySQL Interview Questions. SQL and MySQL are database-related languages. While SQL is a programming language used to work with data in relational databases, MySQL is an open-source database product that implements the SQL standard.

3. What is PRIMARY KEY in MySQL?

The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values and cannot contain NULL values. A table can have only ONE primary key, and in the table, this primary key can consist of single or multiple columns (fields).

4. What is MySQL used for?

Databases are the essential data repository for all software applications. For example, whenever someone conducts a web search, logs in to an account, or completes a transaction, a database system stores the information to access it in the future.

5. What is full MySQL size?

MyISAM tables have a default limit of 256TB for data and index files, which you can change to 65,536TB maximum. InnoDB’s maximum table size is 256TB, corresponding to the full tablespace size.