1. Which SQL clause is used to filter records?
- a) WHERE
- b) HAVING
- c) GROUP BY
- d) ORDER BY
Answer: A - The
WHERE clause filters records before any groupings are made.
2. What is the primary purpose of an SQL INDEX?
- a) To speed up data retrieval
- b) To enforce data integrity
- c) To allocate storage space
- d) To create backups
Answer: A - Indexes improve query performance by creating a quick lookup path.
3. Which SQL command permanently removes a table?
- a) DROP TABLE
- b) DELETE TABLE
- c) TRUNCATE TABLE
- d) REMOVE TABLE
Answer: A -
DROP TABLE deletes the table structure and its data permanently.
4. What does SQL's ACID stand for?
- a) Atomicity, Consistency, Isolation, Durability
- b) Accuracy, Consistency, Integrity, Durability
- c) Atomicity, Concurrency, Isolation, Durability
- d) Automation, Consistency, Isolation, Durability
Answer: A - ACID properties ensure reliable transaction processing.
5. Which join returns all records from the left table?
- a) LEFT JOIN
- b) INNER JOIN
- c) RIGHT JOIN
- d) FULL JOIN
Answer: A -
LEFT JOIN returns all left table records, matched or not.
6. What is the default sorting order of ORDER BY?
- a) ASC (Ascending)
- b) DESC (Descending)
- c) Random
- d) Depends on the database
Answer: A -
ORDER BY sorts in ascending order unless specified otherwise.
7. Which constraint ensures column values are unique?
- a) UNIQUE
- b) PRIMARY KEY
- c) FOREIGN KEY
- d) CHECK
Answer: A - The
UNIQUE constraint prevents duplicate values in a column.
8. Which function calculates the number of rows?
- a) COUNT()
- b) SUM()
- c) AVG()
- d) MAX()
Answer: A -
COUNT() returns the number of rows matching a criteria.
9. What does DML stand for in SQL?
- a) Data Manipulation Language
- b) Data Modeling Language
- c) Database Management Language
- d) Data Migration Language
Answer: A - DML includes
SELECT, INSERT, UPDATE, DELETE.
10. Which operator checks for NULL values?
- a) IS NULL
- b) = NULL
- c) == NULL
- d) NULL()
Answer: A -
IS NULL is the correct way to test for null values.
11. What is the purpose of GROUP BY?
- a) To group rows by column values
- b) To filter groups
- c) To sort results
- d) To join tables
Answer: A -
GROUP BY aggregates data by one or more columns.
12. Which command rolls back a transaction?
- a) ROLLBACK
- b) UNDO
- c) REVERT
- d) CANCEL
Answer: A -
ROLLBACK undoes changes made in the current transaction.
13. What does a FOREIGN KEY constraint do?
- a) Links two tables via a referenced primary key
- b) Ensures unique values in a column
- c) Automatically increments values
- d) Encrypts column data
Answer: A - Foreign keys enforce referential integrity between tables.
14. Which wildcard matches any sequence of characters?
- a) %
- b) _
- c) *
- d) ?
Answer: A -
% matches zero or more characters in LIKE clauses.
15. What is a subquery?
- a) A query nested inside another query
- b) A backup query
- c) A temporary table
- d) A stored procedure
Answer: A - Subqueries are SELECT statements used within another SQL statement.
16. Which command modifies existing data?
- a) UPDATE
- b) ALTER
- c) MODIFY
- d) CHANGE
Answer: A -
UPDATE changes existing records in a table.
17. What is the purpose of HAVING?
- a) To filter groups after GROUP BY
- b) To filter rows before grouping
- c) To sort results
- d) To join tables
Answer: A -
HAVING filters aggregated data, unlike WHERE.
18. Which SQL function combines strings?
- a) CONCAT()
- b) MERGE()
- c) JOIN()
- d) COMBINE()
Answer: A -
CONCAT() merges two or more strings into one.
19. What does SQL's TRUNCATE TABLE do?
- a) Removes all rows but keeps table structure
- b) Deletes the table permanently
- c) Archives table data
- d) Renames the table
Answer: A -
TRUNCATE is faster than DELETE for removing all rows.
20. Which clause removes duplicate rows?
- a) DISTINCT
- b) UNIQUE
- c) GROUP BY
- d) HAVING
Answer: A -
DISTINCT eliminates duplicate values in the result set.