MySQL Interview Questions and Answers
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Best MySQL Interview Questions and Answers
Worldwide data has been increasing at an alarming rate and demand for the data has been increasing tremendously over the years. Worldwide business organizations are giving utmost importance to this constantly generating data because of the value that it holds and helps them in making valuable business decisions. There are many database systems to store and manage this type of vast amount of data and there is MySQL. MySQL is one of the top database management systems available in the market today. If you are about to start your career in MySQL and about to attend an MySQL interview then here are the frequently asked MySQL Interview Questions and Answers. By mastering this top MySQL interview question you will gain knowledge and confidence to clear any interview in the very first attempt.
Top MySQL interview questions and Answers
MySQL is the second most popular database management system in the world with more than 11 million installations globally. It is an open-source platform. MySQL not only performs the relational database management tasks but it also coordinates with different operating systems and makes the functionality successful. There are plenty of jobs available in the market for MySQL professionals. This blog covers MySQL interview questions and answers for fresher’s and experienced. It also covers the MySQL basic to advanced interview questions. All these MySQL interview questions are the commonly asked interview questions in any MySQL interview and act as a medium to land you in your dream job.
These MySQL interview questions are collected and presented here in this blog based on the opinion and suggestion of experienced MySQL and database management professionals. There are huge employment opportunities from the top 100 fortune companies. MySQL is one of the widely used relational database management tools and the number of installments has been growing tremendously because of its unique features and ability to manage data in an effective way. All these lists of MySQL interview questions and answers are designed in a way to simplify your learning process by using clear examples and use cases.
By studying these top MySQL interview questions many students and professionals have got into their dream career. This advanced MySQL interview questions blog covers all the essential concepts related to data querying, sorting data, data filtering, joining tables, data grouping, common table expressions, subqueries, set operators, transactions, constraints in MySQL, globalization concepts, import and export, and advanced concepts. Without wasting any extra time let’s get into the frequently asked MySQL interview questions and answers suitable for freshers as well as experienced.
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This MySQL interview questions and answers blog has been divided into 3 types for making the learning simple. Which are:
Basic MySQL interview questions and Answers
- MySQL Server’s default port is 3306.
- The standard default port is TCP/IP 1433.
Following are the MySQL technical specifications:
- High performance
- Flexible structure
- High availability and replication
- Easy to manage
- Manageable
- Storage management
- High-security standards
- MySQL Enterprise Monitor
- Graphical tools
- Drivers
- JSON support
- MySQL Enterprise Security
- Replication and high availability
- Geo-Spatial support
- OLTP and transactions
The following table gives you a clear view of the core differences between SQL and MySQL:
SQL | MySQL |
It is a standard query language | It is a database |
It acts as a communication tool to interact with database systems like MySQL. | It stores all types of data in a structured format and makes it secured. |
It is a computer language | MySQL is an application or software |
It is used for the creation of database management systems | MySQL is being used for activities like data handling, deleting, sorting, and modifying data. |
Following are the core differences between a table and a database:
Table | Database |
The table is a part of Database | The database is stored and consists of a list of tables |
It represents a portion of data | The database contains tables that store the data. |
Tables are used to group the data that is related to each other | The data stored in the tables in any form becomes part of the database. |
A table is a collection of rows and columns and helps in storing the data in an organized format | The database is a collection of tables and provides an easy to use interface to access the data stored in tables. |
Following are the essential elements that have brought a huge hit to the MySQL server:
- MySQL is open-source software and freely available for developers and small scale organizations.
- It has great community support and the solution for each query is solved very quickly.
- MySQL has been in the market for a very long period and has very stable versions available. All the bugs are neatly removed and makes sure the update is efficient and bugs free.
- It is highly useful, simple to use, and most importantly reliable.
- MySQL software is easy to use and freely downloadable from the internet.
By default, we have many tables available in MySQL. Following are the widely used and notable tables available in MySQL:
- Merge
- MyISAM
- Heap
- ISAM
- InnoDB
Installing MySQL software in a system would allow us to efficiently develop, drop, and test web apps by causing no effect on the websites’ live data. We have multiple ways to use MySQL on our system but the efficient and simple way is to install it manually. Manual installations help the users in getting a clear knowledge about the system and helps in gaining more control over the database.
Manual installation of MySQL brings us the following benefits:
- Data transfer from one location to others in just seconds
- Backing up, and reinstalling will become easier
- It gives you full control over how and when MySQL servers start and end.
- The MySQL software can be installed anywhere. For example, a portable USB drive.
Black Box Testing is associated with the evaluation of the integration of databases to test the functionality. All the test case scenarios involved in Database Black Box Testing are simple and verifies incoming and outgoing data from the function. We have various techniques involved in testing the applications which include boundary-value analysis, equivalence partitioning, graphing technique, etc.
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TEXT: It is being used in MySQL server to store string values and the maximum length of the characters it holds is 65,535. We have four types of TEXT data types in MySQL:
- TEXT
- TINY TEXT
- MEDIUM TEXT
- LONGTEXT
BLOB: The abbreviation is a Binary Large Object and it stores a variable amount of data. BLOB holds up to 65,535 bytes of data. Below mentioned are the BLOB types:
- TINYBLOB
- MEDIUMBLOB
- BLOB
- LONGBLOB
The cursor is mainly used in the MySQL server to handle a result set in the stored procedures. It acts as a pointer to point a specific row from the list of rows. It also acts as a traversal over the records stored in a table and performs traversing actions such as retrieval, addition, and removal of records in a database.
A Null value is defined as a field that contains no value. It is not possible to compare a NULL value with any other NULL values so you can not use the comparison operators like <, =, or >. In order to compare the fields with NULL values, you need to use the operators such as IS NULL and IS NOT NULL.
In order to display the maximum salary or any Maximum number, we use a built function called MAX().
The following table gives you clarity about the differences between the database and GUI testing.
Database Testing | GUI Testing |
It is also considered as Backend testing or Data testing. | It is a Front-end testing or user interface testing |
Deals with the items that are invisible to the user. | Handles the items that are visible. |
Database testers need to have proficiency in testing. | GUI testers need not know about GUI testing. |
It works for the front-end data integrity using the data stored in the backend. | It majorly focuses on the Outlook or outer appearance of an application. |
CTE is abbreviated as Common Table Expression (CTE) and this expression consists of a group of temporary results specified in an SQL statement.
DDL: The abbreviation for DDL is Data Definition Language and it handles the database schemas and also describes how data resides in the database. The most relevant example for DDL is to CREATE TABLE command.
DCL: The abbreviation is Data Control Language and consists of commands like REVOKE, GRANT, etc.
DML: The DML is abbreviated as a Data Manipulation Language and consists of commands such as INSERT, SELECT, etc.
MySQL uses joins to query data from multiple tables. The join query works based on the relationship between the different columns in a table. In MySQL we have four types of joins and which are:
Inner Join: It returns the rows if it finds even a single match between two tables.
Full Join: It will return rows even if there is one match in the tables.
Left Join: Even though there is no match found in the right table it returns all the rows from the left table.
Right, join: It returns all the rows from the right table even if there is no match found in the left side table.
Following are the typical MySQL functions:
- NOWO: This function is intended for returning the current date and time as one value.
- CONCAT (X, Y): This has been used for concatenating two string values that produce a single string output.
- CURRDATEO: It returns the current time and date.
- DATEDIFF (X, Y): it returns the difference between two dates.
The CHAR and VARCHAR commands work together in MySQL to make the table perfect with the right number of columns. The CHAR command is used to define the fixed length of tables and columns. The table length ranges between 1-255. The VARCHAR command is helpful in adjusting the table according to the needs.
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Intermediate SQL Interview Questions and Answers:
Using a Drop Table statement we can delete a table in MySQL. This process would release complete data of a table which also includes the definition and structure of a table from the database permanently. So it is very essential to think twice before deleting a table because once the table gets deleted you can not recover the data or table anymore in MySQL. Following is the command for dropping a table:
Command: ROP TABLE table_name;
The major purpose of the foreign key is to integrate one or more tables. Foreign keys match the primary keys of two different tables to link them together. It helps us in creating parent-child relationships between the tables. Following are the two different ways to add a foreign key to a table:
- ALTER TABLE Statement
- CREATE TABLE Statement
These two fetches are similar but only one variation separates them. MySQL_fetch_array returns an array whereas MySQL_fetch_object returns an object. This indicates that you are not allowed to access the data by using their offsets but you can do it by using field names.
The major functionality of the primary key in MySQL is to identify the rows of a table in a unified way. Each table consists of only a single primary key. The candidate key can be any columns or list of columns that are unique keys in a database. A table can contain multiple candidate Keys in a single table. All the candidate’s keys can be qualified as a Primary key.
Below mentioned are the Triggers that are allowed in MySQL:
- BEFORE INSERT
- BEFORE UPDATE
- BEFORE DELETE
- AFTER INSERT
- AFTER UPDATE
- AFTER DELETE
MySQL slow query log generally contains huge information. Sometimes the query has to be listed hundreds of times. In order to simplify the slow query log problem, we use a third-party tool called ‘pt-query-digest’.
When you lose the root password and if you want to change it then you give it to DB with skip-grants-table and next we can change the password. After changing the password the user is required to start the DB in a normal mode.
DELETE TABLE: DELETE TABLE is generally a logged operation and each row deleted gets logged. So the process becomes a bit slower than usual.
TRUNCATE TABLE: This also deletes the rows the same as the DELETE TABLE command but does not log the rows deleted by it. The process is a bit faster when compared to the DELETE TABLE command.
The Transaction in MySQL is a logical unit of work in which either all tasks or no steps will be performed. ACID is a property of any transaction and ACID stands for Atomicity, Consistency, Isolation, and Durability.
Yes, the Join clause in MySQL would allow us to join two or more tables together. We have multiple types of joins in MySQL. All these clauses are used to connect different tables and return the tables that match the similar property and value in all tables. Following are the different joins which allow us to join the tables in MySQL:
- Left Join
- Inner Join
- Right Join
- Cross Join
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In order to Update a table or records in a table, you have to use the UPDATE statement that is presented in WHere and SET clauses. Using the SET clause we can change the values of a targeted column. The WHERE clause is optional and can be used to define a condition. Using this statement we can also modify values in multiple rows of a single row or multiple rows at the same time.
MySQL is an advanced Graphic User Interface or visual database designing tool deployed for working on MySQL databases. Workbench is a product of Oracle and supports tasks such as SQL development, user administration, data migration, data backup, etc. We can also utilize it for the creation of E-R diagrams, physical data models, and SQL development. It can be used on all the popular operating systems. Workbench is supported by the MySQL server version v5.6 and all the versions after it.
Workbench is currently available in the following editions:
- Community Edition
- Enterprise Edition
- Standard Edition
MySQL is a single or a collection of fields that are being used to identify every record in a table uniquely. A primary key should contain some or other value but it should not be empty or null. We can use the ALTER TABLE statement to delete or remove a primary key from the table.
To drop the primary key we use the below syntax:
ALTER TABLE table_name DROP PRIMARY KEY;
A USER in MySQL is considered as a record in the USER_TABLE. A USER TABLE contains user information such as account privileges, login information, and data to access and manage databases. We can use the MySQL Create User statement to create a new user account in the database. It provides SSL/TLS, authentication, role, resource-limit, and password management properties for the new accounts.
Below mentioned is the syntax for the creation of a new user in MySQL:
CREATE USER [IF NOT EXISTS] account_name IDENTIFIED BY ‘password’;
We have advantages and disadvantages using MySQL and let’s discuss advantages first:
Advantages:
- Provides a secure environment for database management. We can execute all types of database tasks in a secure way.
- MySQL has become a fast and efficient database management system because of its ability to support a wide range of storage engines.
- With its impeccable power, it can process millions of queries.
- Easy to manage and efficient processing
- Unique features like deadlock identification, Executing multiple transactions
Disadvantages of MySQL:
- MySQL suites better for the large databases
- Scalability is a tedious task
- Instability of software.
By using the create statement we can create the following objects:
- DATABASE
- FUNCTION
- EVENT
- TABLE
- PROCEDURE
- INDEX
- VIEW
- USER
- TRIGGER
We have four types of non-standard string types in MySQL which are:
- MEDIUMTEXT
- LONGTEXT
- TEXT
- TINYTEXT
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Advanced MySQL Interview Questions:
- The best practices to follow in using MySQL varies from person to person, following are the popular practices that are followed by the majority of professionals.
- Use the column list in INSERT statements.
- Do not prefix stored procedure names with “sp_”.
- Use ANSI-Standard JOIN Clauses instead of Old style clauses.
- Avoid using queries along with the SELECT statement.
- Try not to use column numbers in the ORDER BY clause.
- Avoid using double quotes in the T-SQL code.
- Avoid using column numbers in the ORDER BY Clause.
- Use aliases if your SQL statement at times when your SQL statements involve multiple sources.
Following are the multiple ways using which you can create an index:
- You can make use of T-SQL statements to create an index.
- Through SQL Server Management studio. Here you can browse to the table for which you want to create the index then right-click on the indexes node. Now you can select the new index option.
- You can also indirectly identify the index by defining the UNIQUE constraint and the PRIMARY KEY within the ALTER TABLE or CREATE TABLE statement.
Following are the core differences between the two tables:
Temporary Table | Heap Table |
This table is valid only during the session. | These tables reside in the memory |
These tables are not shared with any client | Heap Tables can be shared among a wide range of clients |
As temporary tables are storage engines and require no extra privileges. | Temporary tables require a special privilege to create tables. |
Below mentioned are the core differences between MySQL and MongoDB.
MySQL | MongoDB |
It is an open-source relational database management system | It is an Open Source database that is designed for documents like JSON which varies in structure. |
Each record gets stored as a row in a table | Each record will be stored in a document format |
All same types of records are stored in a table | Documents related to a specific class or a group stored in the collection. |
Normalization is a technique used to organize data to eliminate redundancy and data duplication. Normalizations are associated with multiple successive levels and are called general forms. Following are the three different types of normalization forms available in MySQL:
- First Normal Form (1NF)
- Second Normal Form (2NF)
- Third Normal Form (3NF)
Below mentioned are the various types of collation sensitivity:
- Kana Sensitivity
- Case Sensitivity
- Accent Sensitivity
- Width Sensitivity
An access control list is a group of permissions associated with an object. It also acts as a basis for the server security model of MySQL and helps in tackling issues like users access denial.
MySQL stores all the ACLs in the cached memory. If a user tries to run a command or authenticate, immediately MySQL verifies the authentication data and permissions against the ACLs.
The database Whitebox testing handles the elements like data model, tables, referential integrity rules, schema, ACID properties, database consistency, logical views, and triggers.
Federate tables allow users to access the tables on a different database and on a different server.
In MySQL using a configurable variable which is max_heap_table_size can control the size of a Heap table.
The other name for the storage engines is table types and all the information can be stored in files format by employing different techniques.
Various techniques involved:
- Locking levels
- Storage mechanism
- Capabilities and functions.
- Indexing
Below mentioned is the list of Drivers available in MySQL:
- PHP Driver
- ODBC Driver
- PYTHON Driver
- RUBY Driver
- Ado.net5.mxj
- JDBC Driver
- C WRAPPER
- PERL Driver
- CAP11PHP Driver
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