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How to Measure Query Processing Time Without Returning Rows

· One min read
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.)