dbas Interview Questions and Answers

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100 Interview Questions and Answers for DBAs

  1. What is a database?

    • Answer: A database is a structured set of data organized and accessed electronically from a computer system. It's designed for efficient storage, retrieval, modification, and deletion of data. Different database management systems (DBMS) use different organizational methods, such as relational, NoSQL, or object-oriented.

  2. Explain normalization in databases.

    • Answer: Normalization is a database design technique that organizes data to reduce redundancy and improve data integrity. It involves dividing larger tables into smaller tables and defining relationships between them. This reduces data anomalies (insertion, update, deletion) and improves data efficiency.

  3. What are ACID properties?

    • Answer: ACID properties are crucial for database transactions to ensure data integrity. They stand for: Atomicity (all changes in a transaction occur or none do), Consistency (transactions maintain data validity), Isolation (concurrent transactions appear to execute serially), and Durability (committed transactions survive system failures).

  4. What is a database index?

    • Answer: A database index is a data structure that improves 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. Indexes are similar to the index in the back of a book; they allow the database to quickly locate rows matching specific criteria without having to scan the entire table.

  5. Explain different types of database joins.

    • Answer: Common database joins include INNER JOIN (returns rows only when there is a match in both tables), LEFT (OUTER) JOIN (returns all rows from the left table and matching rows from the right table), RIGHT (OUTER) JOIN (returns all rows from the right table and matching rows from the left table), and FULL (OUTER) JOIN (returns all rows from both tables, matching where possible).

  6. What is a stored procedure?

    • Answer: A stored procedure is a pre-compiled SQL code block that is stored in the database. It can accept input parameters, perform database operations, and return results. They improve performance by reducing network traffic and offer enhanced security by encapsulating database logic.

  7. What is a trigger?

    • Answer: A database trigger is a procedural code that is automatically executed in response to certain events on a particular table or view in a database. For example, a trigger could be set to automatically update another table whenever a row is inserted into the primary table.

  8. What is a view?

    • Answer: A database view is a virtual table based on the result-set of an SQL statement. It does not contain any data itself; instead, it provides a customized way to access data from underlying base tables. Views can simplify complex queries and enhance data security by restricting access to specific columns or rows.

  9. What is data integrity?

    • Answer: Data integrity refers to the accuracy, consistency, and reliability of data. Ensuring data integrity is crucial for making informed decisions and preventing errors. Techniques like normalization, constraints, and transactions help maintain data integrity.

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