# 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?  
➡️ 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.

![](https://miro.medium.com/v2/resize:fit:1236/0*1UoE8j3SpwNK3K-V align="left")

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