Mysql Interview Questions

Last update: 19 Jan 2020, 78 QuestionsAsk Question
A Quick Overview of MySQL
Mysql Interview Questions

MySQL is one of the widely used open-source database platforms in the world today. According to mysql.com website, this platform is trusted by the world’s 10 top sites that are considered trustworthy and are frequency visited. Overviewing these MySQL Interview Questions for experienced as well as individuals and the other crucial factors mentioned here can be remarkably result oriented for candidates and new learners to this niche.

What is MySQL? It the most popular Open Source database management system, is developed and supported by Oracle Corporation.
Latest Version 8.0.19 released in 14th December 2019
Created By Oracle Corporation.
Written in C and C++ language
About License GNU Public License
Official Website https://www.mysql.com

Best Mysql Interview Questions And Answers

1. DDL

In MySQL, DDL is the short form for Data Definition Language, which is used in database schemas and descriptions while deciding how data should reside in the database.

Here’s a list of DDL Queries:
  • DROP

2. DML

DML is a short form for Data Manipulation Language which is used in data manipulation and mostly includes common SQL statements to store, modify, retrieve, delete and update data in a database.

Here is the list of DML Queries:
  • CALL

3. DCL

DCL is a short form for Data Control Language including commands which are concerned with User rights, permissions and other controls within the database system.

Here’s a list of queries for DCL:

Mysql is not case sensitive. Its case-sensitivity relies on the underlying operating system as OS determines the case sensitivity of tables names and database. In windows, database and table names are not case sensitive but in the case of UNIX, it is case sensitive in nature. Especially on the UNIX host, database accepts the upper case and lower-case table names.

In MySQL, the time period cardinality refers to the specialty of facts values that can be put into columns. It is a type of property that influences the potential to search, cluster and kind data.

Cardinality can be of two sorts which are as follows
  • Low Cardinality − All values for a column have to be the same.
  • High Cardinality − All values for a column ought to be unique.

The standard way to perform case insensitive queries in SQL is to use the SQL upper or lower functions like the following:

select * from users where upper(first_name) = 'AJAY';


select * from users where lower(first_name) = 'ajay';

The method is to make the field you are searching as uppercase or lowercase then also make the search string uppercase or lowercase as per the SQL function.

Primary Key Unique Key
A table can hold only one primary key It can be more than one unique key in one table
A Primary Key cannot be NULL. A Unique key can have NULL.

These are most commonly used storage engine in MySQL are MyISAM and InnoDB.

Difference between MyISAM and InnoDB are given below:-

  • MyISAM does no longer support transactions, however InnoDB supports transactions.
  • MyISAM helps Table-level Locking, however InnoDB supports Row-level Locking.
  • MyISAM helps full-text search, however InnoDB does not.
  • MyISAM designed for the need for speed but InnoDB designed for most performance.
  • MyISAM does now not aid overseas keys, but InnoDB helps foreign keys.
  • We can use commit and rollback with InnoDB however not in MyISAM.
  • MyISAM does no longer assist ACID (Atomicity, Consistency, Isolation, and Durability) however InnoDB supports the ACID property.
  • In the InnoDB table, the AUTO_INCREMENT field is a section of the index but now not in MyISAM.
  • MyISAM stores its tables, data, and indexes in disk area the usage of a separate table name.FRM, desk name.MYD and table name.MYI however InnoDB stores its tables and indexes in a tablespace.

The default port is 3306. We can change it in /etc/MySQL/my.conf there is a port variable. We can update this port according to our need

MySQL -u username -p database_name < file.sql
Here username is your database username like "root," database_name is your database name, file.sql is your SQL file name with complete path.

Primary Key Candidate Key
It is a column that uniquely identifies a record. In Mysql, only one candidate key can behave like Primary Key. It can be any column that can qualify as a unique key in the database. In MySQL, there can be multiple candidate keys in one table. Each candidate key can behave like as a primary key.

In Mysql, a trigger is a database object that is directly associated with a table. It will be activated when a defined action is executed for the table. It can be performed when you run one of the following MySQL like INSERT, UPDATE and DELETE occurred in a table. It's activation time can be BEFORE or AFTER



mysql> delimiter //


mysql> delimiter ;

SELECT * FROM EmployeeTable1 AS Emp1 WHERE (1) = ( SELECT COUNT(DISTINCT(Emp2.amount)) FROM EmployeeTable2 AS Emp2 WHERE Emp2.amount > Emp1.amount)

NOW() give you the current date time in the format 'YYYY-MM_DD HH:MM: SS' CURRENT_DATE() will only give you the current date in format "YYYY-MM_DD"

Comparisons operators are used to comparing one expression to another value or expression. It is just like = , < , > , => , =<, <>

  • It removes all rows from a table.
  • It does not require a WHERE clause.
  • Truncate cannot be used with indexed views.
  • It is performance wise faster.
  • It removes Some or All rows from a table.
  • A WHERE clause is used to remove particular rows according to the matched condition. All rows will be deleted when we did not use Where condition in Query.
  • It removes rows one by at a time.
  • It can be used with indexed views.
  • It removes a table from the database.
  • All table's rows, indexes, and privileges will also be removed when we used this command.
  • The operation cannot be rolled back.

It is used to concatenate two or more strings.


SELECT CONCAT('BestInterview', ' ', 'Question') AS 'Name';

IS NULL checks to see if the cell is empty but IS NOT NULL checks to see if the cell is not empty.

Example :

SELECT id FROM users WHERE 'user_type' IS NOT NULL;

SELECT id FROM users WHERE 'user_type' NOT IS NULL;

Note: This is very essential MySQL query interview questions.

In MySQL, standards-based drivers for JDBC, ODBC, and .Net are provided in order to enable developers in building database applications with their language of choice.

Following is a list of drivers available in MySQL:

  • PHP Driver
  • JDBC Driver
  • ODBC Driver
  • PYTHON Driver
  • PERL Driver
  • RUBY Driver
  • CAP11PHP Driver
  • Ado.net5.mxj

In MySQL, a trigger corresponds to a set of actions running automatically when a particular change operation like SQL INSERT, UPDATE, or DELETE query is performed on a table.

You can either write command in MySQL like this:



     IF NEW.amount < 0 THEN
        SET NEW.amount = 0;
     ELSEIF NEW.amount > 100 THEN
       SET NEW.amount = 100;
     END IF;

Here’s a code script to convert string data to UTF 8 in your database:

header('Content-Type: text/plain; charset=utf-8');
$databasesToConvert = [ 'database1' */ ];
$typesToConvert = [ 'char', 'varchar', 'tinytext', 'mediumtext', 'text', 'longtext'];
CONVERT(CAST(CONVERT(`{$column}` USING english) AS binary) USING utf8)";
$query = "UPDATE `{$table}` SET " . join( ', ', $converts );
echo "\n", $query, "\n";
echo "\n";


MyISAM Dynamic MyISAM static
This is a table storage format which is basically used when some columns in the existing tables use variable data types such as VARCHAR, BLOB, TEXT, VARBINARY, etc.) This is also a table storage format which is basically used when all columns in the existing table’s uses fixed width data types.
The representation of data in MongoDB is totally different from Mysql, as in MongoDB data is represented in the collection of JSON documents.
MongoDB is an object-oriented database
The representation of Mysql database is totally different form Mongodb, as in Mysql data is stored in the form of tables (Row and columns).
Mysql is a structured query database.
Related Article: SQL Interview Questions

I order to validate the email addresses in Mysql, below mentaioned query is used –
SELECT * FROM `users` WHERE `email` NOT REGEXP '^[^@][email protected][^@]+\.[^@]{2,}$';

Binary data can be stored in Mysql in different ways such as

  • The short length of binary data can be stored in the form of string as a VARCHAR
  • A BLOB data type allows users to store an arbitrary amount of binary data.


Regex is an operational and powerful pattern that can help the users for the implementation of a powerful search utility function for database systems. Moreover, it is an operator which is used when we require matching regular expressions. In addition to this, it also supports a wider range of meta-characters which allow flexibility and more control over the database structure when performing pattern matching.



Match beginning of string(^):

SELECT name FROM users WHERE name REGEXP '^bestinterviewquestion';

It returns the total length of the string which is measured in bytes. It returns the total length of the strings measured in characters.

In MySQL, an ENUM is actually a string object whose value is selected from the list of permitted values pre-defined during the time of a column creation. It is used because it provides compact data storage in addition to readable queries and output.

Here’s the difference between an ENUM and a SET

The value should be one listed in the column definition or internal numeric equivalent. Must be an empty string consisting of values listed in column
mysql_fetch_array() mysql_fetch_row() mysql_fetch_object()
This returns an array of strings corresponding to a fetched row, or FALSE if there are no rows. It returns with a numerical array of strings corresponding to a fetched row, or FALSE if there are no rows. This returns with an object, or a FALSE value if there are no rows.
The returned array type depends on how result_type is defined Here, the row is returned as an array. This fetches a result row as an object type.

The optimized query can be written with the use of the following clause- ‘where’, ‘order-by’ and group-by’. Apart from theses clause like statements with union clause is also used for the optimization of the queries.

In general slow query, the log is basically used in Mysql for the determination of which database queries will take a long duration to run. Moreover, a slow query log in MySQL simplifies that operations in the context of efficient and time-consuming queries.

In order to enable the slow query log the command- Get global slow_query_log – ‘ON’; is used

There are a number of unique features that are incorporated in Mysql 8 include-

  • Unicode 9.0 support
  • Window functions
  • Recursive SQL syntax statements
  • Support Native JSON data
  • Support for document store Functionality

It is a table that points to a table in another MySQL database instance. It can be seen as a view of this remote database. Other RDBMS have the same concepts for example database links.

The maximum size of the HEAP table can be controlled by the MySQL config variable called max_heap_table_size.

MySQL is one of the widely used open source database platforms in the world today. The data in a MySQL database is stored in the form of tables, which consist of many columns and rows. It is a reliable, stable and robust platform with advanced performance and security features.

MySQL is used for a wide range of purposes like data warehousing, e-commerce, web applications, and logging applications.

It is developed by David Axmark.

The first version of MySQL was released on 23 May 1995.

It is a language but not a Programming Language. It is a relational database management system.

  • Data Security
  • It is used to retrieve large amounts of records from a database quickly and efficiently.
  • On-Demand Scalability
  • High Performance
  • Excellent Uptime
  • Reduced Total Cost of Ownership

Storage engines are Mysql components, that can handle the operations for different table types to store and manage information in a database.

  • InnoDB
  • MyISAM
  • CSV
  • ARCHIVE etc

ALTER TABLE EnterTableName ENGINE = EnterEngineName;

SELECT id, GROUP_CONCAT(department SEPARATOR ' ') AS department FROM employee group by id;

Mysql supports various data types. Some most common used data types are given below:-

  • CHAR
  • TEXT
  • INT
  • DATE
  • TIME
  • ENUM

Between operator is used to select a range of data between two values. It can be texts, numbers, and dates, etc.

Syntax: Select * from TABLENAME where FIELDNAME between VALUE1 and VALUE2

IN operator is used to check for a value in the given set of values.

Syntax: Select * from TABLENAME where FIELDNAME IN ('VALUE1','VALUE2',...)

You can use this query in your phpmyadmin SELECT version();

The MySQL aggregate function performs a calculation on a set of values, and it returns a single value as output. It ignores NULL values when it performs calculation except for the COUNT function.


MySQL provides many aggregate functions that are listed below.

  • AVG()
  • COUNT()
  • SUM()
  • MIN()
  • MAX() etc

Functions are generally used for computations, but procedures are usually used for executing business logic.

The function returns only 1 value, but the procedure can return multiple values.

The function can be called directly by SQL statement like select functionName from dual, but procedures cannot be called directly.

The function can be used in the SQL Query directly, but a procedure can not be used in a SQL query.

In Mysql, joins are used to retrieve data from multiple tables. It is performed whenever two or more tables are joined.

There are three types of MySQL joins:-

    SELECT columns FROM table_1 INNER JOIN table_2 ON table_1.column = table_2.column;
    SELECT columns FROM table_1 LEFT JOIN table_2 ON table_1.column = table_2.column;
    SELECT columns FROM table_1 RIGHT JOIN table_2 ON table_1.column = table_2.column;
  • CHAR can have a maximum of 255 characters, but VARCHAR can hold a maximum of 65,535 characters.
  • CHAR field is a fixed length, but VARCHAR is a variable length field.
  • CHAR uses static memory allocation, but VARCHAR uses dynamic memory allocation.

You can use
CREATE INDEX [index name] ON [table name]([column name]);

SELECT std_id, COUNT(std_id) as cnt FROM Student GROUP by std_id having cnt > 1

SELECT id, name, department FROM Employee where MOD(id,2) = 1

It is a procedure stored in a database which can be called by the database engine and connected programming languages. A procedure has a name, a parameter list, and SQL statement, etc. It introduced in MySQL 5.

SELECT * FROM 'TableName' WHERE 'status' = 1 LIMIT 10

SELECT EmpId, Project, Salary, COUNT(*)
FROM EmployeeSalary
GROUP BY EmpId, Project, Salary



SELECT * FROM EmployeeSalary
SELECT * FROM ManagerSalary


WHERE term is used for filtering rows, and it applies to every row but HAVING term is used to filter groups.

WHERE can be used without the GROUP BY but HAVING clause cannot be used without the GROUP BY.

These are the set of rules applied to columns on the table. It is used to bound the type of data that can go into a table.

Types of constraints
  • Not NULL


// Here name is the field & Users is the Table name

  • Kana Sensitivity
  • Case Sensitivity
  • Accent Sensitivity
  • Width Sensitivity etc

HEAP tables are in memory. No TEXT or BLOB fields are allowed inside HEAP tables. They are typically used for high-speed transient storage.

In MySQL, a temporary table is a distinct type of table that approves you to save a transient end result set, in which you can reuse countless instances in a single session. A brief table is created with the aid of the use of the CREATE TEMPORARY TABLE statement.

  • Don't use "sp_" while creating stored procedure.
  • Dont use "*" while you are using SELECT command. Also avoid unnecessary columns in SELECT clause.
  • You can use table aliases while writing queries.
  • Avoid the usage of the wildcard (%) at the starting of a predicate.
  • DISTINCT and UNION need to be used solely if it is necessary.

It is the best way to upload large CSV files through the LOAD DATA command.


LOAD DATA LOCAL INFILE "your file name"

INTO TABLE table name



A database index is the structure of a fact that improves the velocity of operations in a table. It can be created the usage of one or greater columns, presenting the foundation for each fast random lookups and efficient ordering of getting admission to records. Indexes are used to locate rows with specific column values quickly.

The degree of a table is the number of columns in the given table. It is also called as Arity. It is the range of entities inside each entity type that can be linked via a given relationship type.

Timestamp in MySQL

Timestamp in MySQL is used when users want to convert the value from the current time zone to UTC zone for the sake of storage or UTC time zone to the current time zone for retrieval.

DateTime in MySQL

DateTime in MySQL is used to insert values ‘yyyy-mm-dd’ in the table where yyyy is the year, mm is the month and dd is the date. This keyword is used to retrieve or to display DATETIME values in Mysql.

The view is basically a virtual table which is used to view certain and preferable rows or columns of the table. In practice, users can add a number of SQL functions, JOIN and WHERE clause to view the present data of the table.

In MySQL, the CREATE VIEW statement is used to create a new view inside the database.

Here’s the basic syntax of the statement:

CREATE VIEW productList AS SELECT qty, price, totalprice AS value FROM product;

The data in a MySQL database is stored in the form of tables, which consist of many columns and rows. It is a reliable, stable and robust platform with advanced performance and security features.

Development History of MySQL

The first version of MySQL was released in May 1995 by a Swedish company MySQL AB.

To get into complete detail of MySQL interviews, we are mentioning some of the essential MySQL Interview Questions and Answers for experienced. Go through the issues as they will help you.

Advantages of MySQL
  • Data Security
  • On-Demand Scalability
  • High Performance
  • Excellent Uptime
  • Lowered TCO (Total Cost of Ownership)
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