MySql Advance Interview Question with Answer - Part 2
MySql Advance Interview Question with Answer - Part 1
1. What is normalization in MySQL, and why is it important?
Answer: Normalization is the process of organizing data
in a database to reduce redundancy and improve data integrity. It involves
breaking up large tables into smaller, more manageable tables and defining
relationships between them. Normalization helps to avoid data inconsistencies,
improve query performance, and simplify database maintenance.
2. What is a foreign key in MySQL,
and how is it used?
Answer: A foreign key is a column or combination of
columns in one table that refers to the primary key of another table. It is
used to define a relationship between two tables and enforce referential
integrity. When a foreign key is defined, MySQL will ensure that the referenced
data exists before allowing data to be added or updated.
3. What is the difference between a
stored procedure and a function in MySQL?
Answer: A stored procedure is a set of SQL
statements that performs a specific task, while a function is a set of SQL
statements that returns a value. Stored procedures are used to encapsulate
business logic, automate tasks, and improve performance, while functions are
used to perform calculations or manipulate data. Functions can be used in
SELECT, WHERE, and HAVING clauses, while stored procedures cannot.
4. What is a transaction in MySQL,
and how is it used?
Answer: A transaction is a sequence of SQL
statements that are executed as a single unit of work. It allows for multiple
SQL statements to be executed atomically, either all succeeding or all failing,
ensuring data integrity. Transactions are used to ensure that a series of
database operations are completed successfully or rolled back if an error
occurs.
5. What is the difference between
MyISAM and InnoDB storage engines in MySQL?
Answer: MyISAM is a non-transactional storage
engine that is used for read-heavy applications, such as web applications or
data warehousing. It supports full-text indexing, but does not support foreign
keys or transactions. InnoDB is a transactional storage engine that is used for
write-heavy applications, such as e-commerce or banking systems. It supports
foreign keys, transactions, and row-level locking.
6. What is a trigger in MySQL, and
how is it used?
Answer: A trigger is a set of SQL statements that
are automatically executed in response to a specific database event, such as an
insert, update, or delete operation. Triggers can be used to enforce data
integrity, audit data changes, or perform complex business logic. They can be
defined at the table level and are executed before or after the triggering
event.
7. What is a subquery in MySQL, and
how is it used?
Answer: A subquery is a query that is embedded
within another query. It is used to retrieve data that will be used in the main
query, either as a filter or as a value in a calculation. Subqueries can be
nested within other subqueries and can be used in SELECT, WHERE, and HAVING
clauses.
8. What is a join in MySQL, and how
is it used?
Answer: A join is a SQL operation that combines
rows from two or more tables based on a related column. It is used to retrieve
data from multiple tables and create a single result set. Join types include
inner join, left join, right join, and full outer join, and the type used
depends on the desired output.
9. What is indexing in MySQL, and
how is it used?
Answer: Indexing is the process of creating data
structures that improve the performance of queries on a database table. It
involves creating an index on one or more columns in a table, which allows
MySQL to quickly locate the rows that meet the query criteria. Indexing can be
used to speed up queries, enforce data integrity, and reduce the amount of disk
I/O.
10. What is a cursor in MySQL, and
how is it used?
Answer: A cursor is a database object that is used
to manipulate data in a result set, one row at a time. It is typically used in
stored procedures or triggers to process large amounts of data. Cursors can be
used to navigate through a result set, update or delete rows, or perform
complex calculations. Cursors can be declared, opened, fetched, and closed.
11. What is a temporary table in
MySQL, and how is it used?
Answer: A temporary table is a table that is
created and exists only for the duration of a database session or transaction.
It is used to store intermediate or temporary results that are used in a query
or calculation. Temporary tables can be created using the CREATE TEMPORARY
TABLE statement and are automatically dropped at the end of the session or
transaction.
12. What is the difference between a
view and a table in MySQL?
Answer: A view is a virtual table that is created
by defining a SELECT statement as a named object in the database. It is used to
simplify queries, hide complexity, and restrict access to certain data. A
table, on the other hand, is a physical object that stores data in a database.
Views are read-only and do not store data, while tables can be updated,
deleted, or inserted into.
13. What is a deadlock in MySQL, and
how is it resolved?
Answer: A deadlock is a situation where two or more
transactions are waiting for each other to release resources, such as locks on
database objects. It can cause the database to become unresponsive and can lead
to data inconsistencies. Deadlocks can be resolved by killing one of the
transactions or by modifying the application logic to avoid the conflicting
access patterns.
14. What is a full-text search in
MySQL, and how is it used?
Answer: A full-text search is a search technique
that allows for matching text based on relevance, rather than just exact
matches. It is used to search for words or phrases within a large amount of
text data, such as articles, documents, or emails. Full-text searches can be
performed using the MATCH() AGAINST() syntax, which returns results based on a
relevance score.
15. What is a materialized view in
MySQL, and how is it used?
Answer: A materialized view is a precomputed result
set that is stored in a table and updated periodically based on changes to the
underlying data. It is used to improve query performance and reduce the amount
of computation needed to generate complex reports or data sets. Materialized
views can be created using the CREATE MATERIALIZED VIEW statement and refreshed
using the REFRESH MATERIALIZED VIEW statement.
16. What is the difference between
MyISAM and InnoDB storage engines in MySQL?
Answer: MyISAM and InnoDB are two different storage
engines used in MySQL. MyISAM is the default storage engine in MySQL and is
known for its fast performance, but it doesn't support transactions or
referential integrity constraints. InnoDB is a more feature-rich storage engine
that supports transactions, foreign keys, and row-level locking, but it can be
slower than MyISAM for some types of queries.
17. What is a stored procedure in
MySQL, and how is it used?
Answer: A stored procedure is a precompiled SQL
statement that is stored in the database and can be executed on demand. It is
used to encapsulate complex business logic, improve performance, and simplify
application development. Stored procedures can be called from other SQL
statements or programming languages and can have input and output parameters.
18. What is the purpose of the
EXPLAIN command in MySQL, and how is it used?
Answer: The EXPLAIN command is used to show the
execution plan for a SELECT statement in MySQL. It shows the order in which
tables are accessed, the indexes used, and the join type used. This information
can be used to optimize the query and improve performance.
19. What is a database transaction in
MySQL, and why is it important?
Answer: A database transaction is a set of SQL
statements that are executed as a single unit of work. It is used to ensure
data consistency and integrity by guaranteeing that all of the statements in
the transaction are either committed or rolled back as a single operation.
Transactions are important for applications that require atomicity,
consistency, isolation, and durability (ACID) properties.
20. What is a foreign key in MySQL,
and how is it used?
Answer: A foreign key is a constraint that is used to enforce referential integrity between two tables in MySQL. It ensures that a value in one table matches a value in another table's primary key. Foreign keys can be used to prevent orphaned records, maintain data integrity, and simplify database queries. They can be defined using the FOREIGN KEY constraint.
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