15 MySQL Interview Questions & Answers For Beginners & Experienced in 2021

Have a Data engineering or data science interview coming up? Have to practice a few of the most requested MySQL interview questions? The article compiles the record of the MySQL interview questions that you must know. 

Frequent MySQL Interview Questions & Answers

1. What’s MySQL?

MySQL is among the hottest open-source DBMS (database management system). MySQL is straightforward to make use of, dependable, and fast. A DB management system that works on embedded methods in addition to client-server systems. 

2. Why is MySQL so widespread? 

Initially, MySQL is open-source. Second, it’s extensively adopted, so quite a lot of code is already accessible. Even total developed methods are there that can be referred to for the upcoming initiatives. MySQL has relational databases; therefore it makes it have methodical storage quite than a giant dump of unorganized mess. And eventually, as stated earlier, MySQL is fast and sturdy. 

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3. What are the tables in MySQL? Clarify the types.

This can be a must-know MySQL interview query. Let’s see the answer-

MySQL stores every thing in logical tables. Tables can be considered the core storage construction of MySQL. And therefore tables are often known as storage engines. Listed here are the storage engines offered by MySQL:

· MyISAM – MyISAM is the default storage engine for MySQL. It extends the previous ISAM storage engine. MyISAM affords huge storage, as much as 256TB! The tables may also be compressed to get additional storage. MyISAM tables usually are not transaction-safe. 

· MERGE – A MERGE desk is a virtual table that consolidates totally different MyISAM tables which have a comparable construction to 1 table. MERGE tables use the indexes of the bottom tables, as they don’t have indexes of their very own.

· ARCHIVE – Because the name suggests, Archive helps in archiving the tables by compressing them, in-turn decreasing the storage space. Therefore, you may store quite a lot of data with the Archive. It makes use of the compression-decompression process whereas writing and studying the table records. It’s done utilizing the Zlib library.

· CSV – That is extra like a storage format. CSV engine stores the values within the Comma-separated values (CSV) format. This engine makes it simpler to migrate the tables right into a non-SQL pipeline.

· InnoDB – InnoDB is essentially the most optimum whereas selecting an engine to drive performance. InnoDB is a transaction-safe engine. Therefore it’s ACID-compliant and might efficiently restore your database to essentially the most stable state in case of a crash.

· Memory– Memory tables have been previously often called HEAP. With memory tables, there generally is a performance increase because the tables are saved within the memory. But it surely doesn’t work with massive data tables as a result of same reason.

· Federated – Federated tables enable accessing distant MySQL server tables. It can be carried out with none third-party integration or cluster technology.

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4. Write a question for a column addition in MySQL

For this, an ALTER TABLE question is required. As soon as invoked, merely point out the column and its definition. One thing like this:

ALTER TABLE cars

ADD COLUMN engine VARCHAR(80) AFTER color;

5. What’s a foreign key? Write a question to implement the identical in MySQL.

A foreign secret is used to attach two tables. A FOREIGN KEY is a field (or assortment of it) in one table that alludes to the PRIMARY KEY in one other desk. The FOREIGN KEY requirement is utilized to forestall activities that may crush joins between tables.

To assign a foreign key, it is very important mention it whereas creating the table. It may be assigned by invoking the FOREIGN KEY question. One thing like this:

FOREIGN KEY (Any_ID) REFERENCES Table_to_reference(Any_ID)

6. What’s MySQL workbench?

MySQL Workbench is a sure collectively visual instrument for database modelers, designers, and DBAs. MySQL Workbench supplies Data modelling, SQL, and server setup set of administrative tools. To place it merely, MySQL workbench makes it attainable to function the database management system via GUI. 

7. How does database import/export work in MySQL?

It may be carried out in two methods. One is to make use of phpMyAdmin, and the second is to make use of the command line access of MySQL. The latter might be carried out by utilizing the command named mysqldump. It goes one thing like this:

· mysqldump -u username -p databasename > dbsample.sql

To import a database into MySQL, only an indication change is required, with a command of MySQL. The command goes one thing like this:

· mysql -u username -p databasename < dbsample.sql

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8. How can we delete a column or a row in MySQL?

Now dropping a column might be merely carried out by utilizing the ALTER TABLE command after which utilizing the DROP command. It goes one thing like this:

ALTER TABLE table_name DROP column name;

To drop a row, first, an identification for the row is required. As soon as that’s helpful, use the DELETE command at the side of the conditional WHERE command. One thing like this:

DELETE FROM cars WHERE carID = 3;

9. What are the alternative ways to affix tables in MySQL?

Be part of is used to link a number of tables collectively, with the widespread column’s values in each table. Primarily there are 4 varieties of joins:

1. Inner Join – Inner join makes use of a join predicate, which is a situation used to make the join. Right here is the syntax:

SELECT one thing FROM table name INNER JOIN one other table ON condition;

2. Left Join – Left join additionally requires a join situation. The left join chooses data starting from the left table. For every entry within the left table, the left compares every entry in the right table. Right here is the syntax:

SELECT one thing FROM tablename LEFT JOIN one other table ON situation;

3. Right Join – Opposite to left join and, with one distinction within the query, that’s the name of join. Right here care needs to be taken concerning the order of tables. Right here is the syntax:

SELECT one thing FROM tablename LEFT JOIN one other table ON situation;

4. Cross Join – Cross join has no join situation. It makes a cartesian of rows of each the tables. Right here is the syntax:

SELECT one thing FROM tablename CROSS JOIN one other table;

Note: Whereas dealing with just one table, self-join can be possible. 

It is among the most handled MySQL interview questions. Interviewers do wish to see if the candidate understands the fundamentals or not and be a part of one of the core ideas. 

10. Can a major key be dropped in MySQL? If sure, how?

Sure, it’s attainable to drop the primary key from a table. The command to make use of is once more, the ALTER TABLE adopted by DROP. It goes like this:

ALTER TABLE table_name DROP PRIMARY KEY;

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11. What are Procedures in MySQL?

Procedures (or saved procedures) are subprograms, similar to in a daily language, embedded within the database. A saved process consists of a reputation, SQL statement(s) and parameters. It utilizes the caching in MySQL and therefore saves time and memory, similar to the ready statements. 

12. What’s a trigger in MySQL?

A trigger is a table-associated database object in MySQL. It’s activated when a specified motion takes place. 

A trigger might be invoked after or earlier than the occasion takes place. It may be used on INSERT, DELETE, and UPDATE. It makes use of the respective syntax to outline the triggers. For instance, BEFORE INSERT, AFTER DELETE, and so on.

13. How to add customers in MySQL?

To easily put, the person can be added by utilizing the CREATE command and specifying the required credentials. First, log in to the MySQL account after which apply the syntax. One thing like this:

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

Customers might be granted permissions, by the next instructions:

GRANT SELECT ON * . * TO ‘testuser’;

14. What’s the core distinction between Oracle and MySQL?

The core distinction is that MySQL works on a single-model database. Which means it may possibly only work with one base structure, whereas Oracle is a multi-model database. It means it may possibly assist varied data models like graph, doc, key-value, and so on. 

One other basic distinction is that Oracle’s assist comes with a price tag for industrial options. Whereas MySQL is open-source.

Now this query is among the MySQL interview questions that needs to be understood rigorously. As a result of it immediately offers with the industry requirements and what the corporate wants.

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15. What’s CHAR and VARCHAR in MySQL?

Each of them outline a string. The core distinction is that CHAR is a fixed-length whereas VARCHAR is variable size. For instance, if CHAR(5) is defined, then it wants precisely 5 characters. If VARCHAR(5) is defined, then it may possibly take at most 5 characters. VARCHAR might be stated to have extra effectivity within the usage of memory as it can have dynamic memory allocations.