ANSI SQL Test

This skill focuses on retrieving specific data from a database, applying filters to narrow down results, and performing basic aggregations on datasets. It delves into the use of WHERE clauses, conditional logic, and aggregate functions such as SUM(), COUNT(), AVG(), MIN(), and MAX(). Mastering this area ensures that the individual can generate meaningful insights from raw data through simple to moderately complex queries. Intermediate and advanced questions involve multi-step queries and advanced filtering techniques.

Joins and set operations form the backbone of relational database querying, allowing for the combination of data from multiple tables. This skill tests the understanding of various types of joins, including INNER, LEFT, RIGHT, and FULL, and their application in real-world scenarios. It also covers set operations such as UNION, INTERSECT, and EXCEPT, which are used to combine or filter results from multiple queries. The topic ranges from simple joins to complex multi-table joins and advanced set operations in nested queries.

Subqueries, also known as inner or nested queries, are a powerful SQL feature that allows users to embed one query inside another. This skill tests the ability to write subqueries to perform operations that require multiple steps of data retrieval or manipulation. It also evaluates understanding of correlated subqueries, where the inner query relies on the outer query for execution. Complex questions will involve multiple levels of nesting and the use of subqueries in SELECT, INSERT, UPDATE, and DELETE operations.

This skill assesses proficiency in Data Manipulation Language (DML) operations such as inserting, updating, and deleting data. It also evaluates knowledge of transaction management, which ensures database consistency and integrity through commands like BEGIN, COMMIT, and ROLLBACK. The focus extends to the ACID properties (Atomicity, Consistency, Isolation, Durability) that govern how transactions are handled in relational databases. Advanced questions assess the ability to manage complex transactions and resolve concurrency issues in multi-user environments.

Normalization is critical to database design as it reduces data redundancy and improves data integrity. This skill evaluates the understanding of normalization rules (up to 3NF) and the design of well-structured databases. Questions will assess the ability to apply these principles in designing efficient relational databases, understanding the impact of normalization on query performance, and recognizing the trade-offs between normalization and denormalization in real-world scenarios. Advanced questions cover relational schema optimization.

Indexing is key to improving the performance of SQL queries, especially in large datasets. This skill assesses knowledge of different indexing strategies (e.g., clustered, non-clustered) and their impact on query performance. It covers the use of EXPLAIN and ANALYZE commands to understand query execution plans and identify performance bottlenecks. The questions range from basic indexing concepts to complex query optimization techniques, including the use of indexes in conjunction with query tuning strategies for improving speed and efficiency.

Stored procedures, user-defined functions, and triggers are critical for automating repetitive tasks and enforcing business logic at the database level. This skill covers the creation, optimization, and execution of stored procedures and functions. It also explores how triggers can be used to automatically execute actions in response to events within a database. The questions assess both the understanding of syntax and the ability to implement best practices for writing efficient, reusable, and secure stored procedures and triggers.

Advanced SQL features such as window functions (ROW_NUMBER(), RANK(), LEAD(), LAG()) and views offer powerful tools for solving complex analytical problems. Window functions allow for calculations across a set of table rows related to the current row, providing a more flexible alternative to aggregation. Views simplify complex queries by encapsulating them within virtual tables. This skill evaluates the ability to use these constructs for efficient data manipulation and reporting. Advanced questions focus on optimizing window functions and complex view structures.

This advanced skill covers the management of transactions in multi-user environments, with a focus on isolation levels (READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE) and concurrency control. It also tests the understanding of distributed databases, including techniques such as partitioning, sharding, and replication. Advanced questions assess the ability to manage distributed transactions and ensure database consistency and availability in distributed systems, as well as handling deadlocks and transaction failures.