Generating a Random Number in BigQuery

UpdatedMarch 2, 2026

•1 min read

Constantin Lungu

Part of seriesPractical SQL

If you're looking to generate a random number in BigQuery, check out the RAND() function.

It's a pseudo-random number generator, generating a float in the interval [0, 1).

I've used it a few times before, but for the today's exercise, I've decide to try something akin to Python's random.pick(). So, let's pick a random value from an ARRAY.

Inspired by one of Mikhail Berlyant's SO answers (which are some of the best answers on BigQuery on SO, linked in comments), I wanted to randomly assign one of 20 options to 100 participants.

As seen in one of my previous posts about accessing array elements, we're going to generate a random 0-based index to retrieve the random array element in each case.

OFFSET(CAST(ARRAY_LENGTH(available_options)*RAND()-0.5 AS INT64))

Found it useful? Subscribe to my Analytics newsletter atnotjustsql.com.

Comments

Join the discussion

No comments yet. Be the first to comment.

Practical SQL

Part 48 of 50

Short, practical posts on SQL and BigQuery — from core language features to advanced query patterns. A reference for data practitioners at every level.

Up next

Using subqueries with Row Level Security in BigQuery

I've previously posted about row-level security in BigQuery. One of the gotchas back then was the fact that you needed to manually specify what values should the access be filtered for. If only a sub-query was allowed there! Well, a new feature, curr...

More from this blog

BigQuery Saves Your Query Results — Here's How to Find Them

Ever run a heavy BigQuery SQL query, processed gigabytes of data — and then accidentally closed the tab or forgot to save the results? 😬 Don't re-run it. Your results are still there. BigQuery automa

Mar 5, 20261 min read

BigQuery Saves Your Query Results — Here's How to Find Them

Parameters in BigQuery

You can use query parameters in BigQuery hashtag#SQL (now in the console as well!) — but how are they different from variables, and when should you use each? Both parameters and variables act as place

Feb 7, 20261 min read

Flattening JSON arrays in BigQuery

I've noticed that a new JSON function has been added (in Preview) in BigQuery SQL - JSON_FLATTEN(). It allows us to flatten JSON arrays and return a single flat ARRAY, no matter how many nested levels there are. So where is this actually useful?➡️ Ha...

Dec 7, 20251 min read

Using LAST_VALUE with STRUCTS

Even an “empty” STRUCT is still technically something. Not the same as a standalone NULL value. This is why, if you work with STRUCTs in SQL and try to find the latest non-empty struct using LAST_VALUE(...) IGNORE NULLS, you’ll notice it doesn’t help...

Oct 5, 20251 min read

Table grain quick validation with SQL

I was doing some exploratory data analysis on a number of tables I didn’t have much information about and, unfortunately, didn’t know their grain. I needed a quick way to validate my assumptions about the table grain, identify contradicting observati...

Oct 4, 20251 min read

Datawise: A blog on SQL, BigQuery, Analytics, Python Tips and Tricks

204 posts

Data Engineer with a passion for transforming complex data landscapes into insightful stories. Here on my blog, I share insights, challenges, and the ever-evolving dance of technology and business.

Command Palette

Comments

Practical SQL

Using subqueries with Row Level Security in BigQuery

More from this blog