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Start for freeMaster Your Next SQL Interview with These Top 25 Questions
Preparing for an SQL interview can be daunting, especially if you're unsure about the types of questions that might come your way. Tawfiq, an experienced SQL professional, shares his insights in a recent video, outlining the top 25 SQL interview questions based on his extensive career. Whether you're a beginner or looking to brush up on your skills, this guide is tailored to help you excel.
Understanding Basic SQL Concepts
1. DDL and DML Languages:
Understanding the difference between Data Definition Language (DDL) and Data Manipulation Language (DML) is crucial for any SQL user. These form the foundation of SQL coding practices.
2. DELETE vs TRUNCATE:
A common question in interviews is the difference between DELETE and TRUNCATE commands. While both are used to remove data, TRUNCATE is faster and operates differently at a database log level.
Advanced Query Techniques
3. Using CASE Statements:
The CASE statement in SQL functions like an IF-ELSE logic in programming, allowing for conditional operations within your queries.
4. Joins – Inner and Outer:
Knowing how to effectively use various joins like LEFT, RIGHT, FULL OUTER JOIN, and INNER JOIN can significantly impact the data outputs in relational databases.
Optimization and Performance Tuning
5. DISTINCT vs GROUP BY: These commands are used to retrieve unique records from a table; understanding their differences and use cases is vital for efficient query writing.
6. UNION Operator Rules: The UNION operator is used to combine results from multiple SELECT statements but requires that all queries have the same number of columns with similar data types.
Functions and Procedures in SQL
7. Aggregate Functions: The use of functions like SUM, COUNT, MIN, MAX, and AVG helps summarize data sets efficiently. Knowing when to use these functions with or without GROUP BY clauses can be pivotal.
8.Window Functions – RANK vs ROW_NUMBER vs DENSE_RANK: The differences among these functions are subtle but important for managing data sets that require ranked outputs based on specific criteria.
The video also emphasizes the importance of understanding window functions such as LEAD, LAG, FIRST_VALUE among others due to their frequent usage in complex queries.
The importance of preparing for questions on window functions cannot be overstated as they play a crucial role in many advanced SQL operations.
The video further discusses how aggregate functions can also act as window functions using the OVER clause which adds versatility to their application in queries.
The discussion extends beyond just theory; practical examples are provided throughout Tawfiq's blog which he links from his video description ensuring viewers have access to written explanations alongside visual content from his YouTube channel. The video concludes by urging viewers not only watch but also actively participate by trying out examples themselves before checking solutions provided online thus ensuring a hands-on learning experience which is critical when preparing for real-world applications such as interviews or day-to-day tasks at work.
Article created from: https://www.youtube.com/watch?v=AK7_m-aThfw
