Programming

SQL Interview Prep - Programming

This SQL Interview Prep test evaluates your master the core SQL concepts and SELECT query syntax essential for database interviews.

Duration

Complete at your own pace or within the time limit

Questions

Multiple choice with one correct answer

Accuracy

Expert-reviewed questions with clear answer keys

Results

Instant detailed breakdown by topic area

SQL Interview Prep
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About This Test

This test evaluates your understanding of SQL fundamentals and basic SELECT statement construction.

This assessment measures your grasp of SQL basics, including data retrieval, query structure, and the SELECT statement syntax. You'll demonstrate knowledge of how databases store and retrieve information using fundamental SQL commands.

Questions progress from basic syntax recognition to practical query construction scenarios. Each question targets specific SQL concepts with multiple-choice and code-based formats.

Use your results to identify gaps in foundational SQL knowledge and focus your study on weak areas. Stronger scores can suggest comfort with more advanced SQL interview topics.

What This Test Covers

Join Reasoning

Explaining INNER versus OUTER joins, predicting result rows, and handling NULLs from unmatched rows.

Aggregation and Grouping

GROUP BY with HAVING, counting distinct values, and the difference between WHERE and HAVING.

Subqueries and Windows

When to use subqueries versus joins, and solving ranking and top-N problems with window functions.

Database Concepts

ACID properties, transactions, indexes, and normalization asked in technical screens.

Sample Questions

A few real questions from this test, with answers and explanations. Take the full test above for the complete set.

What does a LEFT OUTER JOIN return?

Answer: All rows from the left table, with matching right-table columns or NULLs where no match exists

A LEFT JOIN keeps every row from the left table and fills right-side columns with NULL when there is no match. Matching-only rows describe an INNER JOIN.

What is the key difference between WHERE and HAVING?

Answer: WHERE filters rows before grouping; HAVING filters groups after aggregation

WHERE filters individual rows prior to GROUP BY, while HAVING filters the aggregated groups, so HAVING can reference aggregate functions like COUNT and SUM that WHERE cannot.

Which statement best describes a difference between TRUNCATE TABLE and DELETE (without a WHERE clause)?

Answer: TRUNCATE is typically faster and does not fire per-row triggers, while DELETE logs each row and fires row triggers

TRUNCATE deallocates data pages as a set operation, so it is faster and skips row-level triggers, but it cannot be filtered. DELETE removes rows individually and can use WHERE.

How does UNION differ from UNION ALL?

Answer: UNION removes duplicate rows across the results; UNION ALL keeps all rows including duplicates

UNION performs a distinct operation and eliminates duplicate rows, which costs extra work, while UNION ALL simply concatenates all rows and is faster when duplicates are acceptable.

How does COUNT(column_name) differ from COUNT(*)?

Answer: COUNT(column_name) ignores NULLs in that column; COUNT(*) counts all rows

COUNT(*) counts every row regardless of content, whereas COUNT(column) counts only rows where that column is not NULL. This distinction matters on nullable columns.

Frequently Asked Questions

Find answers to common questions about this assessment

One common approach uses a window function: assign a rank with DENSE_RANK ordered by the value descending, then select rows where the rank equals two. Alternatively, use a subquery selecting the max value below the overall max. The window function approach handles ties clearly and extends easily to the Nth highest.

ACID describes reliable transactions: Atomicity means all steps succeed or none do; Consistency means a transaction moves the database between valid states; Isolation means concurrent transactions do not interfere improperly; Durability means committed changes survive crashes. Together they ensure database operations are trustworthy even under failures and concurrency.

Use a join to combine columns from multiple tables into one result set. Use a subquery when you need an intermediate value, such as filtering by an aggregate or checking existence with IN or EXISTS. Many problems can be solved either way; joins are often faster, while subqueries can be more readable for certain conditions.

A transaction groups one or more statements into a single unit that either fully commits or fully rolls back. This matters for operations that must happen together, like transferring money between accounts. Without transactions, a failure midway could leave data inconsistent. COMMIT saves the work, while ROLLBACK undoes it on error.

Scores are based on the number of correct answers divided by total questions, with a breakdown by topic category.

Yes, questions are randomly selected and ordered from our question bank to ensure each attempt is unique.

No account is required. You can take the test immediately. Optionally provide an email to save your results.

There is no pass/fail threshold. The test measures your knowledge level and provides detailed feedback for improvement.

For knowledge tests, we recommend answering without external help to get an accurate assessment. Practice exercises are designed for learning, so references are acceptable.

Our questions are written for structured educational practice and can give a useful snapshot of your current knowledge in the tested topics.

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