MCQs on Querying Data with ClickHouse | ClickHouse MCQs

Explore ClickHouse MCQ questions and answers designed to test your knowledge on querying data using ClickHouse. This set covers key topics such as SQL syntax, data insertion, query optimization, aggregations, joins, subqueries, window functions, JSON handling, and materialized views. Whether you’re preparing for a test or aiming to improve your ClickHouse skills, these MCQs are perfect for you.

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SQL Syntax in ClickHouse

1. Which of the following is the correct syntax to select all columns in ClickHouse?
   a) SELECT * FROM table;
   b) SELECT ALL FROM table;
   c) SELECT COLUMN * FROM table;
   d) SELECT EVERYTHING FROM table;
2. To filter data based on a condition in ClickHouse, which keyword is used?
   a) WHERE
   b) FILTER
   c) IF
   d) SELECT WHERE
3. In ClickHouse, which command is used to sort query results in descending order?
   a) ORDER BY DESC
   b) SORT BY DESCENDING
   c) DESCENDING ORDER
   d) ORDER DESCENDING BY
4. The correct syntax to limit the number of rows returned in ClickHouse is:
   a) LIMIT 10
   b) RETURN 10 LIMIT
   c) MAXIMUM 10
   d) TOP 10
5. Which of the following is used to group results based on a certain column in ClickHouse?
   a) GROUP BY
   b) SEGMENT BY
   c) CATEGORIZE BY
   d) CLUSTER BY

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Data Insertion and Bulk Imports

6. The correct syntax for inserting data into a ClickHouse table is:
   a) INSERT INTO table VALUES;
   b) INSERT table VALUES;
   c) PUT INTO table VALUES;
   d) ADD INTO table VALUES;
7. To import large datasets from a file into ClickHouse, which command is used?
   a) BULK IMPORT
   b) LOAD DATA INFILE
   c) IMPORT FILE INTO
   d) INSERT FILE INTO
8. Which of the following is the best method to insert data in bulk into ClickHouse?
   a) INSERT INTO using SELECT
   b) INSERT INTO VALUES
   c) INSERT INTO BATCH
   d) COPY INTO
9. When using the INSERT command, what is the default delimiter for CSV files in ClickHouse?
   a) Comma (,)
   b) Semicolon (;)
   c) Tab (\t)
   d) Space ( )
10. In ClickHouse, what does the “INSERT INTO table VALUES (…)” command do?
    a) It updates the table with new data
    b) It deletes all records from the table
    c) It adds new rows of data into the table
    d) It creates a new table with the specified values

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Query Optimization Techniques

11. Which of the following techniques can be used to optimize a query in ClickHouse?
    a) Use of indexes
    b) Use of WHERE clause
    c) Use of JOINs only
    d) Avoiding GROUP BY
12. What is the best way to optimize queries for large datasets in ClickHouse?
    a) Avoid using LIMIT
    b) Use partitions
    c) Increase server memory
    d) Use more joins
13. In ClickHouse, which function helps in optimizing aggregate queries by precomputing values?
    a) Aggregation
    b) Materialized views
    c) Preaggregation
    d) Summarization
14. The use of which feature in ClickHouse can drastically improve query performance when filtering by date?
    a) Indexing
    b) Sharding
    c) Partitioning
    d) Hashing
15. Which of these can improve query speed in ClickHouse by minimizing the amount of data being processed?
    a) Using SELECT DISTINCT
    b) Using WHERE conditions early
    c) Adding JOIN clauses
    d) Avoiding ORDER BY

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Aggregations, Joins, and Subqueries

16. In ClickHouse, which aggregate function is used to find the total sum of a column?
    a) SUM()
    b) COUNT()
    c) MAX()
    d) AVG()
17. What is the purpose of the JOIN clause in ClickHouse?
    a) Combine multiple tables based on a related column
    b) Aggregate data from multiple sources
    c) Create new tables
    d) Filter data based on a condition
18. Which type of JOIN in ClickHouse includes unmatched rows from the right table?
    a) INNER JOIN
    b) LEFT JOIN
    c) RIGHT JOIN
    d) FULL JOIN
19. A subquery in ClickHouse is:
    a) A query nested inside another query
    b) A function used in SELECT statements
    c) A temporary table
    d) A method for table creation
20. The syntax for performing an aggregate query using GROUP BY in ClickHouse is:
    a) SELECT column, AGGREGATE(column) FROM table GROUP BY column;
    b) AGGREGATE column BY GROUP FROM table SELECT column;
    c) SELECT column FROM table GROUP BY column WITH AGGREGATE;
    d) SELECT AGGREGATE(column) FROM table GROUP BY column;

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Working with Arrays and Nested Structures

21. To store multiple values in a single column, ClickHouse provides which data type?
    a) ARRAY
    b) STRUCT
    c) LIST
    d) SET
22. Which function is used to access array elements in ClickHouse?
    a) ARRAY_ELEMENT()
    b) ARRAY_GET()
    c) GET_ARRAY()
    d) ARRAY_INDEX()
23. In ClickHouse, to create an array of integers, which of the following syntax is correct?
    a) [1, 2, 3]
    b) (1, 2, 3)
    c) ARRAY(1, 2, 3)
    d) {1, 2, 3}
24. How do you extract a specific element from a nested structure in ClickHouse?
    a) USE()
    b) UNNEST()
    c) ARRAY JOIN()
    d) SELECT()
25. What does the function arrayJoin() do in ClickHouse?
    a) Joins two arrays into one
    b) Flattens array columns into multiple rows
    c) Removes duplicates from arrays
    d) Sorts arrays

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Advanced Query Features

26. Which function in ClickHouse allows you to execute queries in parallel across partitions?
    a) ParallelExec()
    b) DISTRIBUTED()
    c) Parallelize()
    d) EXECUTE()
27. In ClickHouse, which of the following is a feature used for materialized queries that improve performance?
    a) Indexed views
    b) Pre-computed aggregate queries
    c) Cacheable results
    d) Materialized views
28. The syntax for creating a materialized view in ClickHouse is:
    a) CREATE VIEW AS SELECT…
    b) CREATE MATERIALIZED VIEW…
    c) CREATE VIEW MATERIALIZED…
    d) CREATE TABLE AS SELECT…
29. Window functions in ClickHouse are typically used for:
    a) Ranking data
    b) Filtering duplicate records
    c) Sorting data
    d) Joining tables
30. In ClickHouse, the function rowNumber() is an example of:
    a) A window function
    b) A subquery
    c) An aggregation function
    d) A scalar function

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Answer Key

QNo	Answer (Option with Text)
1	a) SELECT * FROM table;
2	a) WHERE
3	a) ORDER BY DESC
4	a) LIMIT 10
5	a) GROUP BY
6	a) INSERT INTO table VALUES;
7	b) LOAD DATA INFILE
8	a) INSERT INTO using SELECT
9	a) Comma (,)
10	c) It adds new rows of data into the table
11	a) Use of indexes
12	b) Use partitions
13	b) Materialized views
14	c) Partitioning
15	b) Using WHERE conditions early
16	a) SUM()
17	a) Combine multiple tables based on a related column
18	c) RIGHT JOIN
19	a) A query nested inside another query
20	d) SELECT AGGREGATE(column) FROM table GROUP BY column;
21	a) ARRAY
22	b) ARRAY_GET()
23	a) [1, 2, 3]
24	c) ARRAY JOIN()
25	b) Flattens array columns into multiple rows
26	b) DISTRIBUTED()
27	d) Materialized views
28	b) CREATE MATERIALIZED VIEW…
29	a) Ranking data
30	a) A window function