Postgres从JSONB更新INTEGER列

Question

I have a table cart :

 id     | value |     metadata
--------+-------+-------------------
  45417 |     0 | {"value": "1300"}
  45418 |     0 | {"value": "1300"}
 276021 |     0 | {"value": "1300"}

and I'm trying to UPDATE the value column with the value in the JSONB metadata if it exists. I come up with the following query:

UPDATE cart SET value=CAST(subquery.meta_val as INTEGER) FROM
(SELECT id, metadata->>'value' as meta_val FROM cart
WHERE value = 0 AND 
metadata->>'value' IS NOT NULL) as subquery
WHERE cart.id=subquery.id;

Now this works but it takes quite a lot of time for 4M rows I want to update on production and it looks to me like there is a lot of redundancy in the query.

I think the next step would be to wrap all this in a transaction and improve the query, is there anything that can be done to improve performance out of this query ?

Answer 1

Try it without a subquery.

update cart as c
set value = coalesce((c.metadata->>'value')::int, 0)