Flattening JSON arrays in BigQuery

UpdatedMarch 2, 2026

•1 min read

Constantin Lungu

Part of seriesBigQuery Arrays & Structs

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?
➡️ Handling heterogeneous JSON where the nesting depth isn’t consistent
➡️ Cleaning up malformed or jagged arrays
➡️ Normalizing data before UNNEST so you don’t get arrays of arrays

Where I would not use it?

👉 Don’t use it when the hierarchy matters. Flattening removes structural context, so you lose information about where an element came from.

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