Skip to content
⟪
PrepStack
Blog
Interview
.NET
React
SQL
System Design
AI
Azure
Angular
About
Home
Interview
SQL
SQL interview questions
Query design, indexing, transactions, and tuning.
SQL
Easy
SELECT vs SELECT DISTINCT in SQL — when to use which
10 views
SQL
Hard
SQL CTE (Common Table Expressions) — recursive and non-recursive, with examples
4 views
SQL
Medium
Subquery vs JOIN in SQL — performance and readability tradeoffs
4 views
SQL
Medium
What are SQL indexes and how do they actually work?
4 views
SQL
Medium
ACID properties in SQL — explained with examples
4 views
SQL
Hard
How to optimize a slow SQL query — step-by-step debugging approach
5 views
SQL
Easy
WHERE vs HAVING in SQL — what is the actual difference?
4 views
SQL
Hard
SQL window functions — ROW_NUMBER, RANK, DENSE_RANK with real examples
5 views
SQL
Medium
GROUP BY in SQL — explained with real-world examples
4 views
SQL
Easy
INNER JOIN vs LEFT JOIN in SQL — the real difference, with examples
7 views
SQL
Hard
Explain the difference between READ COMMITTED and REPEATABLE READ.
3 views
SQL
Medium
When does a Postgres index NOT get used?
5 views