API design:

POST /db/table/row-pks/-/update
{
   "field": "updated_value"
}

Only the fields that you pass will be updated.

Maybe this is the wrong design though? The design for insert currently looks like this:

• API to insert a single record into an existing table #1851 (comment)

POST /db/table/-/insert
Authorization: Bearer xxx
Content-Type: application/json
{
  "row": {
    "id": 1,
    "name": "New name"
  }
}

I could use the same format for /-/update, but in this case the API doesn't require you to pass every field so "row" doesn't seem like the right key.

I think I'll go with this:

POST /db/table/1/-/update
Authorization: Bearer xxx
Content-Type: application/json
{
  "update": {
    "name": "New name"
  }
}

The benefit of having an "update" key is that it allows me to use other keys in the future. Maybe a "alter": true key to indicate that new columns should be added if they are missing.