SQL Cheat Sheet 2026

The 30 highest-yield SQL facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. In SQL Server, how do you get the top 10 percent of rows? → SELECT TOP 10 PERCENT
2. Why might a DELETE fail due to a foreign key? → Child rows still reference the row being deleted
3. Why will the following SQL query fail? `SELECT ProductName FROM Products WHERE ProductID = (SELECT ProductID FROM OrderDetails WHERE Quantity > 100);` → The subquery returns multiple rows, which cannot be compared using the `=` operator.
4. To reuse a filtered subset of orders in two different joins within one query, a CTE helps by: → Defining the subset once and referencing it by name
5. What does CUME_DIST() compute? → The cumulative distribution: fraction of rows at or below the current value
6. Which SQL command is used to remove all rows but keep the table structure most efficiently? → TRUNCATE
7. A subquery that references a column from the outer query is called what? → Correlated subquery
8. What is a key benefit of using views to simplify complex joins? → Users query one named object instead of rewriting the join
9. How do ROWS and RANGE frame modes differ when there are duplicate ORDER BY values? → ROWS counts physical rows; RANGE groups peers with equal values
10. What is the difference between RANK() and DENSE_RANK() output for values 10,10,20? → RANK gives 1,1,3 and DENSE_RANK gives 1,1,2
11. Which of the SQL commands below deletes all rows in the SalesData table? → DELETE FROM SalesData
12. Which window function returns a value between 0 and 1 representing relative standing? → PERCENT_RANK()
13. Why might you use a window function instead of GROUP BY for aggregates? → To keep individual rows while adding aggregate columns
14. Which clause forces NULL values to appear first in PostgreSQL? → ORDER BY col NULLS FIRST
15. Which clause CANNOT typically contain a subquery in standard SQL? → The keyword list of an INDEX definition
16. Without an ORDER BY clause, the order of returned rows is: → Not guaranteed
17. What is a filtered index (also called a partial index)? → An index built only on rows that satisfy a specified WHERE condition
18. When using EXISTS, what should the subquery's SELECT list typically be? → Irrelevant, often SELECT 1
19. What does PERCENT_RANK() return for the very first row of an ordered partition? → 0
20. In ACID, what does Durability guarantee? → Committed changes survive system failures
21. Which returns rows less than AT LEAST ONE value from the subquery? → < ANY
22. Which gets a single random row efficiently in MySQL? → ORDER BY RAND() LIMIT 1
23. What is the result type of AVG over an integer column in most databases? → A decimal or floating-point value
24. A query needs to select all invoices with an `Amount` between 500 and 1000, inclusive of both values. Which `WHERE` clause correctly represents this condition? → WHERE Amount BETWEEN 500 AND 1000
25. Which clause defines a column that automatically gets a value when none is supplied on INSERT? → DEFAULT
26. Which command permanently saves a transaction's changes? → COMMIT
27. Which statement is used to remove a view from the database? → DROP VIEW
28. Why might WHERE bonus > 0 exclude rows where bonus is NULL? → NULL comparisons yield unknown, not true
29. To extract data from a database, which SQL statement is used? → SELECT
30. Which command adds a new column to an existing table? → ALTER TABLE ... ADD COLUMN