MySQL Interview Questions and Answers for 5 years experience

1. What are the different storage engines in MySQL and their characteristics?

   • Answer: MySQL offers several storage engines, each with strengths and weaknesses. InnoDB is the default, supporting transactions, ACID properties, and row-level locking. MyISAM is faster for read-heavy workloads but lacks transactions and uses table-level locking. Memory (HEAP) stores data in memory, offering extremely fast access but losing data on server restart. Others include Archive (for archiving data), and Blackhole (for discarding data).

2. Explain indexing in MySQL. What are the different types of indexes?

   • Answer: Indexes are data structures that improve the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. Types include B-tree (most common, for equality and range searches), Fulltext (for searching text), Hash (for equality searches only), and spatial indexes (for geographic data).

3. How do you optimize MySQL queries?

   • Answer: Query optimization involves various techniques like using appropriate indexes, optimizing table design (normalization), writing efficient SQL queries (avoiding `SELECT *`), using EXPLAIN to analyze query plans, utilizing query caching, and properly configuring the MySQL server (buffer pool size, etc.).

4. What are transactions and ACID properties?

   • Answer: Transactions are sequences of database operations performed as a single logical unit of work. ACID properties ensure data integrity: Atomicity (all operations succeed or none do), Consistency (database remains consistent after transaction), Isolation (transactions are isolated from each other), Durability (committed transactions survive failures).

5. Explain different types of joins in SQL.

   • Answer: Joins combine rows from two or more tables based on a related column. INNER JOIN returns rows only when there is a match in both tables. LEFT (OUTER) JOIN returns all rows from the left table, even if there's no match in the right. RIGHT (OUTER) JOIN is the reverse. FULL (OUTER) JOIN returns all rows from both tables.

6. What is normalization in database design? Explain the different normal forms.

   • Answer: Normalization is a process of organizing data to reduce redundancy and improve data integrity. Normal forms (1NF, 2NF, 3NF, BCNF, etc.) represent different levels of normalization, each addressing specific types of redundancy. 1NF eliminates repeating groups, 2NF eliminates redundant data that depends on only part of the primary key, and 3NF eliminates transitive dependencies.

7. How do you handle deadlocks in MySQL?

   • Answer: Deadlocks occur when two or more transactions are blocked indefinitely, waiting for each other. Strategies include minimizing the scope of transactions, ordering locks consistently, using lower isolation levels (if appropriate), and monitoring and resolving deadlocks using MySQL's tools.

8. Explain the different isolation levels in MySQL.

   • Answer: Isolation levels control how transactions interact with each other. READ UNCOMMITTED allows dirty reads, READ COMMITTED prevents dirty reads but allows non-repeatable reads and phantom reads. REPEATABLE READ prevents dirty and non-repeatable reads but allows phantom reads. SERIALIZABLE prevents all concurrency issues but can significantly reduce performance.

9. What are stored procedures and how are they beneficial?

   • Answer: Stored procedures are pre-compiled SQL code stored in the database. They improve performance by reducing network traffic, enhance security by controlling access, and promote code reusability.

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