Calculating Average Value of JSONB array in Postgres

All we need is an easy explanation of the problem, so here it is.

I have a column called "value" in my "answers" table.

|  value  |
|---------|
|  [1,2]  |
|   [1]   |
| [1,2,3] |

The type of "value" is "jsonb".

I want to get the average value of each array in each row:

SELECT avg(value) AS avg_value
FROM answers

But this doesn’t work because avg() is not a jsonb function. I’ve tried:

SELECT avg(value::integer[]) as avg_value
FROM answers

i.e. tried to cast the jsonb arrays into integer arrays and then taking the avg, but I get the following error: "cannot cast type jsonb to integer[]. null".

Any ideas?

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

You need to unnest the JSON array with jsonb_array_elements.

You can do this in a correlated subquery:

SELECT
  (SELECT AVG(value::decimal(18,5))
   FROM jsonb_array_elements(value)
  ) AS avg_value
FROM answers;

DB Fiddle

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

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