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SQL interview questions
Query design, indexing, transactions, and tuning.
SQL
Easy
INNER JOIN vs LEFT JOIN in SQL — the real difference, with examples
SQL
Easy
SELECT vs SELECT DISTINCT in SQL — when to use which
SQL
Easy
WHERE vs HAVING in SQL — what is the actual difference?
SQL
Medium
GROUP BY in SQL — explained with real-world examples
SQL
Medium
Subquery vs JOIN in SQL — performance and readability tradeoffs
SQL
Medium
What are SQL indexes and how do they actually work?
SQL
Medium
ACID properties in SQL — explained with examples
SQL
Hard
SQL window functions — ROW_NUMBER, RANK, DENSE_RANK with real examples
SQL
Hard
SQL CTE (Common Table Expressions) — recursive and non-recursive, with examples
SQL
Hard
How to optimize a slow SQL query — step-by-step debugging approach
SQL — PrepStack | PrepStack