If you are preparing for a MySQL interview, the following are the commonly asked question that you can expect in your next interview. We have provided a sample answer for each interview question to help you know how best to respond.
1. Define MySQL.
MySQL is Data Base management system software that can be used by programmers to develop different types of applications mainly web applications. MySQL was developed and distributed by Oracle Corporation. Due to its flexibility MySQL is supported by most operating systems like Linux and Windows. MySQL also uses General Public License that allows a user to download it to develop free applications. For a programmer to develop commercial applications by using MySQL, the programmer needs to buy the MySQL commercial version.
2. Discuss The Advantages And Disadvantages Of Mysql.
MySQL is among the most common database software that is used by modern systems.
The advantages of MySQL include:
- MySQL is believed to be safe to use. The Data Base Management System software can also be quite reliable when it comesto developing new applications.
- The software is also faster and supports different storage engines for storage of data.
- The Data Base Management System software,MySQL, has very easy maintenance and debugging process.
- It can handle several queries at ones and at a very high speed.
- MySQL is compatible to advanced database features like deadlock identification, multi-level transactions and other similar features.
Some of the disadvantages of MySQL include:
- Modifying the MySQL to become more scalable is not easy for developers.
- It cannot handle extremely large database types.
- MySQL has limitations when it comes to using stored routines and triggers.
3. Discuss The Features Of MySQL.
MySQL’s most common features that make the database more popular are.
- It is user friendly, meaning it is easy to navigate.
- Most programmers find it reliable.
- It has a free version for anyone who is interested in using it.
- The software is compatible to several programming languages like: C++, PERL, PHP, Java, and so on.
- The database is also able to support structure Query Language (SQL).
- MySQL is customized in a way to enable the user to modify it according to the developer’soutput expectations of an application.
4. Define The Term HEAP Data And When They Should Be Used.
HEAP data is a special type of table that receives data that is in a heap structure, it is quite useful when data coming into the table is so random and the data is also without any structural order. The HEAP data tables do not have clustered indexes defined on them.
HEAP data is also very useful when there is a need for the removal of the highest or lowest order element. It is also important in sorting large numbers of elements. However, the data stored in this table is temporary and if something was to happen to MySQL causing the software to crash, then the date in the HEAP data will be lost.
5. Define The Term Transaction In MySQL And Explain Its Properties.
Transaction in MySQL is a sequence of statements, queries, or commands in a group for the main purpose of performing a single task. The task can be rolled back or committed. Examples of transactions include select, delete, insert or update. A transition is only complete when all individual operations within a group are successful.
Its properties are:
- Atomicity. These are set rules that guaranteethe reliability of a transaction. The feature dictates whether a transaction will be successful or not.
- Consistency. The system maintains consistency by ensuring any future changes on the data base are accurate for a committed transaction.
- Isolations. The system ensures transparency by conducting transaction tasks independently.
- Durability. The system ensures consistency and durability by focusing on a committed transaction despite any type of system failure.
6. Define The Terms “ Commit” And “ Rollback”
Commit is a transaction statement used by a database after completing the execution of tasks successfully. The transaction command allows the database to make permanent changes. Whereas rollback is also a transaction command that the database executes when one of the transactions in a group is not completed successfully. This command helps the database to cancel any new changes and allows the database to go back to its initial state.
7. Discuss The Difference Between MyISAM And InnoDB
MyISAM and InnoDB are both storage engine types of databases. Database tables are created based on the two storage engines, whereas InnoDB is the default storage engine of MySQL and MyISAM is a non-transactional storage engine. The following are the differences between the two database storage engines.
- InnoDB can handle longer support transactions compared to MyISAM.
- InnoDB supports Row-level Locking unlike MyISAM that supports Table-level Locking.
- MyISAM was designed for the purpose of enhance speed while InnoDB was mainly designed for the purpose of enhancing performance.
- InnoDB aids foreign keys unlike MyISAM which does not support overseas keys
- Commit and rollback commands are acceptable in InnoDB while they cannot be used in MyISAM.
- There is an AUTO_INCREMENT field section of the index of the InnoDB table, which is not found in MyISAM.
- Table data and indexes of MyISAM are stored in the disk area however table data and indexes of InnoDB are stored in a tablespace.
8. Define The Term “MySql TRIGGERS” And Discuss The Six Mysql Table TRIGGERS.
MySql TRIGGERS is a database store program that is automatically executed to respond to a specific command that leads to events such as updating, deletion or insertion. The following are the six MySql table TRIGGERS.
- Before update trigger
This is a trigger that enacts before an updated execution. The moment an update statement is written than implemented the update trigger comes first before the implantation of the update.
- After update trigger
This trigger gets invoked after the implementation of an update in the database.
- Before insert trigger
Before insert trigger is a trigger that is executed before inserting a statement into the database.
- After insert trigger
This trigger is invoked after statement implementation.
- Before delete trigger
This trigger is invoked before deleting an implemented statement.
- After delete trigger
This is the trigger that is invoked after deleting the entire implemented operation.
9. Explain The Scalar And Aggregate SQL Functions.
SQL aggregate functions generate a single value calculated from all the values in one column. The aggregate functions include:
- SUM () – provides the total
- MIN () – provides the smallest value in a column.
- MAX () – provides the largest value in a column.
- LAS () – provides the last value in a column.
- FIRST () – provide the first value of a column.
- COUNT () – provides the number of rows in a column.
- AVG () – provides the average of all the numbers in a selected column.
Scalar SQL functions generate a single value based on the input. The following are the Scalar SQL functions:
- UCASE () – turns a field to an upper case.
- LCASE () – turns a field to a lower case.
- MID () – extracts texts characters from a filed.
- LEN () – returns a text fields length.
- ROUND () – rounds up a numeric field to be nearest number of decimals.
- NOW () – generates the systems current date and time.
- FORMAT () – previews how a field should be displayed.
10. Define DDL, DML, DCL, And TCL In MySQLAnd Explain Their Commands.
Data Definition Language (DDL) decides how data should be residing in database schemas and descriptions. DDL commands include
- CREATE: it creates tables, triggers, functions, index and stored procedures in the data base.
- DROP. Its main function is to delete objects like tables or an entire data base.
- ALTER. It used to alter changes on the existing database structure.
- TRUNCATE. It removes stored table records from the data base.
- RENAME. The command is used when renaming database stored objects.
Data Manipulation Language. (DML) is a command that performs data manipulation of data stored in the server. DML commands include:
- SELECT: this commands allows selection of records from a table.
- INSERT: It allows insertion of data into database file.
- UPDATE: it updates the already existing data in a table.
- DELETE. This command deletes data from the database.
Data Control Language is a programming language that controls the data access permissions of a database. The commands include:
- GRANT. This command allows the user to access the database.
- REVOKE. The revoke command denies the user access to the database.
Transaction Control Language command controls all the database transactions. The commands include.
- COMMIT. The COMMIT command allows the running of a transaction
- ROLLBACK.It rolls back the current transaction back to the starting point.
- SAVEPOINT. It saves a transaction at a particular point so the next the database will begin from that save point to continue with its transactions.
- SET TRANSACTION.It identifies a specific transaction in a group.
11. Explain The Ways In Which You Can Optimize A Mysql Query.
- You should try not use functions in predicates.
- The beginning of your predicate should not start with wildcard like (%)
- Unnecessary column should be avoided when it comes to the select clause.
- DISTINCT and UNION should only be used when it is necessary.
- For sorted results ensure to use ORDER BY clause.
12. Define TheTem Indexing In Mysql.
Indexing is the structure of data modified for the main purpose of speeding the operations in tables. Indexes are also to locate values in rows and columns at a fast speed.
13. What Is The Similarity Between DELETE and TRUNCATE.
They are both commands that delete database records. However, the main differences are DELETE deletes single or multiple records however TRUNCATE can delete the entire record and leave the database empty.
14. Define The Term CHAR In MySQL.
1CHAR is an SQL data type that stores a fixed string of characters of a particular length. When the length is less than the set length the remaining empty part is filled with blank spaces to fill the expected equal length.
15. What Are Other Terms Used In Place Of Mysql Drivers. Also, State The Examples Of Mysql Drivers.
Other terms used to describe MySQL drivers are Connector/ ODBC and MyODBC.
Examples of MySQL drivers are:
- PHP Driver
- JDBC Driver
- ODBC Driver
- C WRAPPER
- PYTHON Driver
- PERL Driver
- RUBY Driver
- CAP11PHP Driver
16. Explain The Difference Between MongoDB And MySQL.
The main difference between MongoDB and MySQL is that data in MongoDB is represented in the collection of JSON documents while data in Mysql is represented in form of tables that contain rows and columns.
The other main difference between MongoDB and MySQL is MongoDB is designed as an object-oriented database, unlike MySQL which is has a query structure design.
17. Define The Term Regex In MySQL.
Regex is an operational pattern that was developed with the purpose of helping users implement search functions in a database system. It matches regular expressions in a wide range of Meta characters, hence giving the user more control over the database when conducting their pattern-matching tasks.
18. How Would You Store Binary Data MySQL?
There are different ways of storing binary data in MySQL, short-length binary data is stored in form of strings like VARCHAR. BLOB data types give the user an option of storing an arbitrary amount of binary data.
19. State The Difference Among Mysql_Fetch_Array (),Mysql_Fetch_Object () Andmysql_Fetch_Row ().
- mysql_fetch_array () responds with arrays of strings on a fetched row. It also responds with a FALSE is there are no visible rows.
- mysql_fetch_row () responds to fetched rows with arrays of strings. If the rows are not available it responds with a FALSE.
- mysql_fetch_object () has an objective response on fetched rows, it also responds with a FALSE if the rows are not visible.
20. What Is The Use Of Enum In MySQL?
An enum is a string with an aim of selecting values from permitted rows and columns. It is quite essential during the creation period of columns since it can be able to read and analyze output and queries.
21. What New Features Does The New Mysql 8 Contain?
Some of the new features that come with the MySQL 8 include:
- Unicode 9.0 support
- Window functions
- Recursive SQL syntax statements
- Support Native JSON data
- Support for document store Functionality
22. Explain The Meaning Of Slow Query Log In Mysql.
Slow query log in MySQL is mainly used in determining the type of database queries that will take longer to run. It simplifies the database operations by separating time-consuming queries into queries that will take a shorter time to be implemented.
23. Differentiate BETWEEN And IN Operators InMysql
BETWEEN selects a range of data between two values. The data may be dates, texts, or numbers. Whereas IN operator checks for a specific value in a given wide range of values.
24. Discuss The Difference Between Function And Procedure In MySQL
- Function responds with a mandatory single value while procedure with a zero or an N value.
- Functions only works with one statement unlike procedure that works with several statements that include select, insert, delete and update.
- It is impossible to work with transactions in function unlike in procedure where transactions are possible.
- It is impossible to handle an error with function however by the help of try-catch, it is possible to handle errors in procedure.
25. Define Both The Primary And Foreign Key And Also Explain Their Differences.
- Primary key: a primary key is used by database table to identify unique rows it is also essential in creating relationships between tables
- Foreign keys. Foreignkey is just a primary key used on another table as a primary key or another different field creating a relationship between the two tables.
The differences between a primary and foreign key include:
- A primary key identifies a unique record whereas a foreign key refers to the primary key of a unique record or table.
- It is impossible for a primary key to accept a NULL value unlike a foreign key that has no problem accepting NULL values.
- As long as a record has been inserted on the table that has a primary key, it is not necessary to insert the same record on a table that has the same primary key as a foreign key.
- When records are deleted from a table that contains a primary key, there is need to delete the same record on another table with similar record as foreign key, however deleting records from a table that contains a foreign key, there is no need of deleting the same record of another table.
Ensure to practice these questions and answers in order to impress the interviewer. Doing so will also increase the chances of getting hired. Besides, dress decently arrives on time for the interview, and respond to every question with confidence. It is also important to check the company’s website to familiarize yourself with certain basic details, which you might be asked.