Mysql Interview Questions For Freshers
"MySQL Interview Questions for Freshers: Get Prepared for Your Upcoming Interview"
MySQL is a widely used open-source relational database management system and new entrants in the field of software development should be familiar with its fundamental concepts and principles. Some common MySQL interview questions for freshers may include querying techniques, database design fundamentals, data types, indexing, and transaction management. Interviewers may also ask about basic SQL syntax, normalization, joins, and data manipulation commands. Additionally, being knowledgeable about database optimization, security, performance tuning, and backup and recovery processes will also be beneficial. Overall, candidates should have a strong understanding of MySQL and its components to demonstrate their competence and potential in the field of database management.
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1 - What is the difference between primary key and foreign key in MySQL?
Answer: Primary key is a unique identifier for a record in a table, whereas foreign key is a column that refers to the primary key of another table. It is used to establish a relationship between two tables.
2) What are different types of joins in MySQL?
Answer: The different types of joins in MySQL are:
Inner join: Returns rows that have matching values in both tables.
Left join: Returns all the rows from the left table and the matching rows from the right table.
Right join: Returns all the rows from the right table and the matching rows from the left table.
Full outer join: Returns all the rows from both tables, regardless of a match.
3) What is the purpose of the “HAVING” clause in MySQL?
Answer: The HAVING clause is used to filter data after the GROUP BY clause has been applied. It enables the user to specify a condition that must be met by the aggregated data.
4) How do you optimize MySQL queries?
Answer: Some ways to optimize MySQL queries are using proper indexes on tables, avoiding the use of wildcards at the beginning of a search, limiting the number of results to be returned, and using EXPLAIN to understand the query execution plan.
5) What is the difference between CHAR and VARCHAR data types in MySQL?
Answer: CHAR is a fixed length data type that can hold a maximum of 255 characters, while VARCHAR is a variable length data type that can hold a maximum of 65,535 characters. VARCHAR uses only the required storage space, while CHAR always uses the specified length, even if the actual data is smaller.
6) What is the function of the “EXPLAIN” statement in MySQL?
Answer: The EXPLAIN statement is used to analyze and show the execution plan of a SELECT statement. It helps in identifying any potential performance issues in the query.
7) How do you backup and restore a MySQL database?
Answer: The most common way to backup and restore a MySQL database is by using the mysqldump and mysql commands, respectively. The mysqldump command exports the database into a file, while the mysql command imports the data from the file into the database.
8) What is the purpose of the “DEFAULT” keyword in a column definition in MySQL?
Answer: The DEFAULT keyword is used to set a default value for a column if no value is specified during insertion. It ensures that the column always has a value, and avoids any errors related to null values.
9) Write a query to retrieve the top 5 records from a table in MySQL.
Answer:
SELECT * FROM table_name LIMIT 5;
10) What is the difference between MyISAM and InnoDB storage engines in MySQL?
Answer: MyISAM is a non transactional storage engine in MySQL, while InnoDB is a transactional storage engine. MyISAM is suitable for read intensive applications, while InnoDB is better for write intensive applications that require data reliability.
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11) What is the “SET” statement used for in MySQL?
Answer: The SET statement is used to assign values to user defined variables in MySQL. These variables can be used within a session to store temporary values.
12) What is the use of the “SHOW” command in MySQL?
Answer: The SHOW command is used to display information about databases, tables, columns, and other objects in a MySQL database. It can also show the status of the server and variables.
13) How can you prevent SQL injection attacks in MySQL?
Answer: SQL injection attacks can be prevented in MySQL by using prepared statements, validating user input, and limiting the privileges of the database user.
14) How do you use the “LIMIT” keyword in a MySQL query?
Answer: The LIMIT keyword is used to limit the number of rows returned by a SELECT statement in MySQL. It takes two arguments, the first being the starting row and the second being the number of rows to be returned.
15) What is the purpose of the “GROUP BY” clause in MySQL?
Answer: The GROUP BY clause is used to group rows with similar data together in a MySQL query. It is usually used with aggregate functions to perform calculations on grouped data.
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