The demand for MySQL in India is significant and continues to grow and industries are looking for skilled professionals to work as database administrators, data analysts, data scientists, software developers, and DevOps engineers. To obtain these roles, you must have strong SQL proficiency, knowledge in database design and modeling, performance tuning, cloud technology understanding, scripting and automation, and so on. Review your skills with this article that covers top 40 interview questions and answers for MySQL. We suggest you review our MySQL Course Syllabus to get started.
MySQL Interview Questions and Answers for Freshers
Here are some interview questions on MySQL for freshers:
1. What is MySQL?
SQL is used to store and manage data in MySQL, a relational database management system (RDBMS). Because it is open source, anybody can use and alter it.
MySQL uses tables with rows and columns to store data. A schema outlines the relationships between tables as well as how data is arranged and stored. Rules controlling the connections between various data fields are enforced by MySQL.
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2. What does MySQL stand for?
“My Structured Query Language” is what MySQL stands for. Data is stored and managed using a relational database management system (RDBMS).
- My: The co-creator’s daughter,
- SQL: Structured Query Language is a programming language for database interaction.
One well-known open-source database management system is MySQL. It is renowned for being quick, dependable, and simple to operate.
Numerous apps use MySQL, such as web-based programs, internet retailers, playing online games, online advertising, point-of-sale systems for retail, monitoring systems, IoT, and so on.
3. What are the advantages of using MySQL?
The relational database management system (RDBMS) MySQL has numerous advantages,
- Scalability: MySQL scales well and can manage massive volumes of data.
- Performance: MySQL’s rapid data processing is well-known.
- Reliability: MySQL is a dependable option for programmers.
- Ease-of-use: MySQL boasts a sizable and helpful community.
- Cross-platform compatibility: Windows, Linux, and macOS are just a few of the operating systems that MySQL is compatible with.
- Security: Security features provided by MySQL include encryption, access limits, and user authentication.
- Cost-effectiveness: MySQL is freely available and adaptable.
- Support: MySQL offers comprehensive documentation and lively discussion boards.
- Replication: MySQL allows replication for high availability and backup.
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4. What is a database?
One tool for organizing and storing data is a database. Information on individuals, goods, orders, and other things can be stored in it.
Types of databases:
- Relational databases like SQL
- NoSQL databases like MongoDB
- Object-oriented databases
- Cloud databases
Data about individuals, goods, orders, and other things can be stored in databases. Information can be arranged using databases. Data can be manipulated and queried using databases.
5. What is a DBMS?
The software tool that enables users to build, manage, and access data in a database is called a Database Management System (DBMS). Large volumes of data are stored, arranged, and retrieved using DBMSs.
In contemporary data-driven applications, database management systems (DBMSs) are crucial for handling massive volumes of data. DBMSs facilitate effective data access and storage for businesses. DBMSs assist businesses in safeguarding private data.
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6. What is a DBMS used for?
DBMS used for:
- Database creation and management: Databases can be defined, created, and managed by users.
- Data storage and retrieval: Users have the ability to store, retrieve, sort, remove, and alter data.
- Assure data integrity: Database management systems (DBMSs) guarantee that data is correct and consistent.
- Control security: To safeguard data, DBMSs employ authentication, encryption, and access controls.
- Support concurrent access: Concurrent access is supported by DBMSs, which let several users access the same database simultaneously.
- Offer backup and recovery: Database management systems (DBMSs) offer options for data backup and restoration.
7. How to check the MySQL version?
There are several tools and techniques you can use to check the MySQL version, such as:
- phpMyAdmin: Locate the MySQL version in the “Database server” section of phpMyAdmin after logging in.
- MySQL Workbench: Click Server and Server Status after connecting to a server with MySQL Workbench.
- dbForge Studio for MySQL: To view the current server version, test your connection.
- MySQL Shell: Log in to MySQL Shell, then type SHOW VARIABLES LIKE ‘%version%’; to view comprehensive version details.
8. What does a MySQL database contain?
A multithreaded SQL server that supports many back ends, a variety of client programs and libraries, administrative tools, and a broad range of application programming interfaces (APIs) make up the client/server system known as MySQL Database Software.
9. List the ways to interact with MySQL.
Method 1: Work using the MySQL shell. To run SQL commands on a Mac or PC, use Terminal or CMD, respectively.
Method 2: Installing the third-party Python library as described below and importing it appropriately into the .py file is required to communicate with this server/database using the Python programming language.
Method 3: Another choice is phpMyAdmin, a web-browser-based interface for MySQL database interaction.
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10. What are the different tables in MySQL?
MySQL supports two types of tables: non-transaction-safe tables (HEAP, ISAM, MERGE, and MyISAM) and transaction-safe tables (InnoDB and BDB).
MySQL Table Types/Storage Engines:
- ISAM.
- MyISAM.
- MERGE.
- InnoDB.
- MEMORY (HEAP) ARCHIVE.
11. What are MySQL Database Queries?
A MySQL database query is a Structured Query Language (SQL) command that tells a MySQL database to do certain things with data, like retrieve, insert, update, or remove data from database tables. In essence, a MySQL database query is a method of accessing and modifying data stored in a MySQL database using a particular syntax.
Example of a simple MySQL query:
SELECT * FROM customers WHERE city = “New York”;
12. What is the purpose of the SELECT statement in MySQL?
The “SELECT” statement is the most popular SQL command for reading data from a database in MySQL. It is used to get data from one or more tables inside a database, effectively enabling you to query and extract specific information from your tables depending on your stated criteria.
Syntax:
SELECT [column_list] FROM [table_name] [WHERE clause] [ORDER BY clause] [LIMIT clause]
13. What is normalization?
The process of arranging data in a database is called normalization. It entails building tables and interactions between them in accordance with guidelines intended to safeguard the data and increase database flexibility by getting rid of redundant and inconsistent dependencies.
14. What are the different data types in MySQL?
Numerous data kinds, including numeric, text, date and time, spatial, and JSON, are supported by MySQL.
- Numeric data types such as integer, decimal, BIT, TINYINT, SMALLINT, MEDIUMINT.
- String data types such as CHAR, VARCHAR, BINARY, VARBINARY.
- Date and time data types such as DATETIME, TIMESTAMP.
- Spatial data types such as points, paths, polygons.
- Other data types such as JSON, SET, BOOLEAN.
15. What are the different storage engines in MySQL?
The underlying software elements that manage SQL operations for various table types are called storage engines. MySQL uses a variety of storage engines, including InnoDB, MyISAM, ISAM, CSV, Archive, Heap, and XtraDB.
16. What is the difference between MyISAM and InnoDB?
MySQL databases use two different storage engines: MyISAM and InnoDB. InnoDB is better for mixed read-write workloads, whereas MyISAM is better for workloads that include a lot of reading.
- MyISAM is quicker for read operations, however it might not function well for frequently updated, large-volume data.
- InnoDB is quicker for highly concurrent and mixed read-write operations.
| Factors | MyISAM | InnoDB |
| Transactions | MyISAM does not support ACID-based transactions. | InnoDB supports ACID-based transactions. |
| Foreign Keys | MyISAM does not support foreign key constraints. | InnoDB fully supports foreign key constraints. |
| Indexing | MyISAM uses full-text indexing. | InnoDB uses full-text, clustered, and adaptive hashing. |
| Crash Recovery | MyISAM has limited crash recovery. | InnoDB has robust crash recovery. |
17. Explain the concept of indexing in MySQL.
In MySQL, indexing is the process of generating pointers to data places in a database so that querying columns is quicker. This improves response times and query efficiency.
- A column or collection of columns is used by MySQL to generate an index, which is a smaller table.
- The key is the set of columns that make up the index.
- MySQL easily locates rows with particular column values by using the index.
- Compared to reading each row one after the other, this is substantially faster.
18. What are the different types of indexes in MySQL?
Numerous index types are supported by MySQL, including:
Primary Key: This index, which is generated automatically when a primary key is defined, gives each table row a unique identity.
Unique: It permits NULL values while guaranteeing that every value in the indexed columns is distinct.
Full Text: utilized for text-based searches, particularly for the columns TEXT, CHAR, and VARCHAR.
Composite: This index, which consists of several columns, enables effective querying using combinations of those columns.
Spatial: Geometry and geography are examples of spatial data types that use this term.
Clustered: This index physically arranges data according to the values of the primary keys in InnoDB tables.
B-Tree: The B-tree enables the index to locate data without searching the full table, speeding up data access.
Descending: Rows are kept in descending order using the descending method.
Invisible: Updated when INSERT, UPDATE, or DELETE commands are executed but not handled by the query optimizer.
Partial: Gives the user control over how much room the index takes up.
Simple: The most popular kind of index, this one only has one column.
19. What is a primary key?
A column, or group of columns, that uniquely identifies every row in a database table is called a primary key. It is employed to guarantee that every table row is unique, which is crucial for preserving data integrity.
20. What is a foreign key?
A column or group of columns in one table that points to a primary key in another is called a foreign key. To create and enforce associations between data in several databases, foreign keys are utilized.
21. What is a unique key?
In a database table, a unique key is a column or group of columns that guarantees every row has a distinct set of values. To avoid duplicate data and guarantee data integrity, unique keys are utilized.
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MySQL Interview Questions and Answers for Experienced
Here are the advanced MySQL interview questions and answers:
1. What is a composite key?
A database table’s composite key is a combination of two or more columns that gives each record a unique identity. Database management systems frequently employ this kind of candidate key.
2. What are the different types of joins in MySQL?
In MySQL, the many kinds of joins are:
- INNER JOIN: Provides data from both tables that match.
- LEFT OUTER JOIN: All rows from the left table plus matching rows from the right table are returned by the LEFT OUTER JOIN.
- RIGHT OUTER JOIN: All rows from the right table plus matching rows from the left table are returned by a right outer join.
- FULL OUTER JOIN: All rows from both tables, including matching and mismatched rows, are returned via a FULL OUTER JOIN.
3. What is the difference between INNER JOIN and LEFT JOIN?
When you wish to get only the rows from both tables that match according to the join condition, use an inner join. To extract all rows from the left table and the matched rows from the right table, use a left join. Non-matching rows should be returned with NULL values.
4. What is the difference between UNION and UNION ALL?
While the UNION ALL statement does not eliminate duplicates from the result, the UNION command joins two or more SELECT statements while eliminating duplicates from the final result set. All records, including duplicates from the SELECT operation, are simply concatenated using UNION ALL.
5. What is the difference between WHERE and HAVING clauses?
The HAVING clause in SQL filters data from groups of rows, whereas the WHERE clause filters data from individual rows.
- WHERE Clause: Based on certain criteria, the WHERE clause filters data from particular table rows. It is useful for merging data from many sources.
- HAVING Clause: The HAVING clause uses conditions with aggregate values to filter data from groups of rows in a query. When used with the GROUP BY clause, it is utilized.
Examples:
WHERE clause:
SELECT username, followers FROM instagram_data WHERE followers > 1000
HAVING clause:
SELECT country FROM instagram_data GROUP BY country HAVING AVG(followers) > 100
6. What is the difference between DELETE and TRUNCATE statement?
The TRUNCATE statement in SQL eliminates every row from a table, whereas the DELETE statement eliminates only certain rows.
- DELETE eliminates particular rows according to predetermined criteria. Duplicate rows, unnecessary data, and data that needs to be cleaned up can all be removed with this command.
- Without the use of criteria, TRUNCATE eliminates every row from a table. Particularly for large tables, this command is quicker than DELETE.
| Factor | DELETE | TRUNCATE |
| Types of Statement | Data Manipulation Language (DML) statements. | Data Definition Language (DDL) statements. |
| Identity of Table | DELETE does not reset the table’s identity. | TRUNCATE resets the table’s identity. |
| Undoing | No option to reverse. | If you haven’t issued a COMMIT, you can use the ROLLBACK command to reverse a TRUNCATE operation. |
7. What is the difference between DROP and DROP TABLE statements?
Two DML commands for working with data in relational databases are DROP TABLE and DROP DATABASE.
- DROP TABLE: To remove an existing table and all of its database records, use the drop table statement.
- DROP DATABASE: The statement removes every table in the database as well as the database itself.
8. How to create a stored procedure in MySQL?
In MySQL, a stored procedure is created using the following syntax. Through parameters, it may return one or more values, or it may not return anything at all. Our present database is automatically linked to a procedure.
However, by giving it the name database_name.procedure_name, we may easily create it from the current database into another database.
DELIMITER &&
CREATE PROCEDURE procedure_name [[IN | OUT | INOUT] parameter_name datatype [, parameter datatype]) ]
BEGIN
Declaration_section
Executable_section
END &&
DELIMITER;
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9. How to create a trigger in MySQL?
The build TRIGGER statement in MySQL allows us to build a new trigger. When utilizing the CREATE TRIGGER command, it is to guarantee that we have trigger privileges. The basic syntax for creating a trigger is as follows:
CREATE TRIGGER trigger_name trigger_time trigger_event
ON table_name FOR EACH ROW
BEGIN
–variable declarations
–trigger code
END;
10. What is the difference between a stored procedure and a trigger?
A single value, a row, or several rows can be returned by stored procedures. A trigger is a stored process that runs in response to a certain event, like the insertion, deletion, or update of a record. A trigger may also be triggered by an update to a particular column. However, triggers are unable to provide a value.
11. What is the difference between a view and a table?
Data in the form of rows and columns is stored in database entities called tables. A view is a virtual table that allows you to see or work with specific areas of the table. Like actual ordered tables, it too has rows and columns.
12. What is the difference between a database and a schema?
A “schema” is the structured blueprint or structure that specifies how the data is arranged within a database, including the relationships between various data elements and tables; it functions similarly to a design plan for the database layout. A “database” is the actual collection of data stored electronically.
13. What is the difference between a clustered index and a non-clustered index?
A non-clustered index is a distinct entity that includes index keys and row locators, whereas a clustered index establishes the order of data in a database.
Clustered Index
- It specifies the arrangement of data in a table,
- It is keeping data rows in line with the clustered index keys.
- Because the data and index are stored together, they are typically smaller.
- They are quicker for ordered data retrieval and range queries.
Non-clustered Index
- Non-clustered indexes are larger than clustered indexes because they hold index keys and row locators independently of the data.
- It is quicker for equality searches and single-row lookups
- They are able can be produced more than once on a same table
- Together, clustered and non-clustered indexes enhance the performance of data retrieval.
14. What is the difference between a partitioned table and a non-partitioned table?
Partitioned Table: A partitioned table is a database table divided into smaller, independent segments called “partitions,” allowing for more efficient data management and querying by enabling operations to be performed on specific subsets of data within the table.
Non-partitioned tables: They store all data in a single unit, requiring full table scans for most queries, which can be significantly slower for large datasets.
15. What is the difference between a subquery and a correlated subquery?
- A correlated subquery depends on the outer query and is executed for each row returned by the outer query as it references columns from the outer query within its own WHERE clause.
- A correlated subquery “re-runs” the subquery with each row of the outer query to check for specific conditions based on the current row’s values.
- A regular subquery is a query nested within another query that operates independently, meaning it calculates its results once before the outer query executes.
16. What is the difference between a cursor and a loop?
- Database objects called cursors let you access and work with data row by row.
- Programming constructs called loops allow you to repeat a piece of code as long as a predetermined condition is met.
17. What is the difference between a temporary table and a permanent table?
- Temporary tables are used for intermediate data storage within a single session, whereas permanent tables store data that needs to be persisted over an extended period of time.
- A temporary table is only present for the duration of a database session and is automatically deleted at the end of the session.
- A permanent table is stored permanently in the database and accessible by multiple users across sessions.
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18. How to optimize a MySQL query?
You can utilize indexes, rewrite queries, and track performance to optimize MySQL queries. Database indexes and server configuration are also modifiable.
Uses of Indexes:
- Make indexes on columns that are commonly utilized in JOIN operations or WHERE clauses.
- Depending on how you query the table, select the indexes.
- Review and update indexes frequently to reflect variations in query patterns and data volume.
Rewrite the queries Reduce superfluous subqueries, streamline intricate joins, improve WHERE clause conditions, and filter data as precisely as you can.
Monitor Performance
- Make use of resources such as query profiler, EXPLAIN, and MySQL Performance Schema.
- Find and fix bottlenecks and slow queries.
- Examine query execution plans to find bottlenecks, inefficient join techniques, or missing indexes.
19. What is the difference between MySQL and MongoDB?
Open-source database management systems (DBMS) for managing and storing data include MongoDB and MySQL. The primary distinction between both is that MySQL is a relational database, whereas MongoDB is a non-relational (NoSQL) database.
| Factors | MySQL | MongoDB |
| Data Structure | It stores information in rows and columns in a structured tabular style. MySQL stores data according to a strict schema. | It stores information in a flexible way as JSON documents. Self-describing MongoDB documents can hold a variety of schemas, including unstructured data sets. |
| Performance | It has memory caches that guard against data loss and a fast transactional mechanism. However, while handling several requests at once, MySQL could encounter lags or mistakes. | It is quicker while adding or editing a lot of records. MongoDB has no downtime when scaling horizontally across several data centers. |
| Use Cases | As it supports structured data, content management systems frequently employ it. Applications that need data security and sophisticated text searches should also use MySQL. | For developers seeking a versatile data model, this is a viable option. Structured, semi-structured, and unstructured data may all be efficiently managed with MongoDB. |
| Scalability | MySQL has limited scalability choices. | MongoDB can scale quickly at a low cost. |
| Query Language | MySQL uses Structured Query Language (SQL). | MongoDB uses JavaScript as a query language. |
20. What is the difference between MySQL and PostgreSQL?
There are two open-source relational database management systems (RDBMS): MySQL and PostgreSQL. Since PostgreSQL is more sophisticated than MySQL, developers frequently choose it.
| Factors | MySQL | PostgreSQL |
| Database Type | A purely relational database. | An object-relational database that supports storing data as objects with properties. |
| Concurrency | MySQL does not support MVCC. | PostgreSQL supports multiversion concurrency control (MVCC) and parallel query plans. |
| Triggers | MySQL does not support triggers. | PostgreSQL supports more sophisticated triggers, including row-level, statement-level, and event-level triggers. |
| Window Functions | MySQL does not support Windows functions. | PostgreSQL supports more advanced window functions, such as LAG(), LEAD(), FIRST_VALUE(), and LAST_VALUE(). |
| Data Types | MySQL does not support advanced data types. | PostgreSQL supports more advanced data types, including arrays and XML. |
| Performance | MySQL is faster and more stable for read-only operations. | PostgreSQL is better for managing read-write operations. |
Conclusion
These interview questions and answers for MySQL will be helpful for you. Depending on the role you are applying for and the organization you are interviewing with, different questions will be asked. It is crucial to be ready to respond to inquiries concerning your familiarity with MySQL and your understanding of its various features and functionalities. Enhance your skills with our MySQL training in Chennai.
