How to Measure Query Processing Time Without Returning Rows

Learn how to use the FORMAT Null option in ClickHouse to measure query processing time without returning any rows to the client.

Question

My query is returning many rows but I’m only interested in the query processing time. How do I omit the query output and check for query processing time?

Answer

Append FORMAT Null to your query to configure the output format to Null. This prevents data from being transmitted to the client.

For example:

SELECT
    customer_id,
    count() AS total,
    any(review_headline)
FROM amazon_reviews
GROUP BY customer_id
ORDER BY total DESC
FORMAT Null

The response will return the number of rows processed and the elapsed time, but 0 rows will be returned:

0 rows in set. Elapsed: 25.288 sec. Processed 222.04 million rows, 13.50 GB (8.78 million rows/s., 533.77 MB/s.)