Mysql Advanced Interview Questions
Mysql Advanced Interview Questions
Mysql Advanced Interview Questions
Mysql advanced interview questions are designed to test the knowledge and expertise of candidates in complex database concepts such as indexing, query optimization, and database performance tuning. These questions require candidates to have a deep understanding of the Mysql database system and be able to troubleshoot and solve intricate database problems. Employers use these questions to assess a candidate's ability to handle high-level tasks and make critical decisions in a fast-paced and constantly evolving database environment. Candidates who can confidently answer advanced Mysql questions demonstrate their proficiency in database management and have a better chance of securing a job in the competitive field of data management.
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1 - What is the difference between a Primary key and a Unique key?
A primary key is a column (or set of columns) that uniquely identifies each row in a table. It cannot contain duplicate values and is used to ensure data integrity and to establish relationships with other tables. Only one primary key can be assigned to a table. On the other hand, a unique key is also used to ensure data integrity and prevent duplicate values, but it can contain null values and multiple unique keys can be assigned to a table.
2) What is a foreign key?
A foreign key is a column or set of columns that references a primary key in another table. It is used to establish relationships between tables and ensure data consistency. A foreign key can only contain values that are present in the primary key it is referencing.
3) Explain the difference between a clustered and non clustered index.
A clustered index orders the data in a table based on the values in the specified columns. It is physically stored in the same order as the index, allowing for faster data retrieval. A table can only have one clustered index. Non clustered indexes, on the other hand, do not change the physical order of the data and instead create a separate list of pointers to the data. A table can have multiple non clustered indexes.
4) What is the difference between an INNER JOIN and a OUTER JOIN?
Inner join returns only the rows that have matching values in both tables based on the specified join condition. Outer join, on the other hand, returns all the rows from one table, even if there are no matching values in the other table. There are three types of outer joins: left, right, and full outer join.
5) What is a view and how is it different from a table?
A view is a virtual table that presents data from one or more tables in a different format. It is stored as a query in the database and can be used like a table for data retrieval. Unlike a table, a view does not contain data physically and is updated automatically as the underlying data changes.
6) What is the purpose of the GROUP BY clause?
The GROUP BY clause is used to group rows with the same values in the selected column(s) and perform aggregate functions on them, such as SUM, COUNT, and AVG. It is often used in conjunction with the HAVING clause to further filter the grouped results.
7) What is a stored procedure?
A stored procedure is a set of SQL statements that are stored in the database and can be executed repeatedly. It can accept input parameters, perform complex data processing and manipulation, and return a result set. Stored procedures are used to improve performance, security, and maintainability of database operations.
8) What are triggers?
Triggers are special types of stored procedures that are automatically executed when a certain event occurs, such as an insert, update, or delete operation on a specific table. They can be used to enforce data integrity, audit changes, or perform additional actions based on certain conditions.
9) What is a subquery?
A subquery is a query nested within another query, used to retrieve data for further processing. It can be placed in the SELECT, FROM, WHERE, or HAVING clause and can be used for filtering, joining, or aggregating data.
10) What is the difference between a stored procedure and a function?
A stored procedure can perform data manipulation and retrieval operations whereas a function can only return a single value or a table variable. Also, a stored procedure can have both input and output parameters, while a function can have only input parameters. Functions can be used in SQL queries, while stored procedures cannot be used in queries.
11) What is a cursor?
A cursor is a database object used to manipulate data row by row. It allows looping through a set of rows and performing operations on each row individually. Cursors are often used in stored procedures for complex data processing.
12) What is a deadlock?
A deadlock occurs when two or more processes are waiting for each other to release locked resources, preventing either one from progressing. This can lead to a situation where the processes are stuck and the database is unable to complete any of the transactions, resulting in a system failure.
13) How can you improve database performance?
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Database performance can be improved by optimizing queries, creating indexes, using stored procedures, and normalized data structures. Proper database design, maintenance, and monitoring can also contribute to better performance.
14) What is an ACID transaction?
ACID stands for Atomicity, Consistency, Isolation, and Durability and it represents the properties of a database transaction. Atomicity ensures that a transaction is either completed fully or not at all, consistency maintains data integrity during transactions, isolation ensures that transactions do not interfere with each other, and durability guarantees that committed changes will persist even in the event of a system failure.
15) What is the purpose of the EXPLAIN statement?
The EXPLAIN statement is used to analyze the execution plan of a query, showing the steps taken by the database to retrieve the requested data. It can help in identifying potential performance issues and suggest ways to optimize the query.
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