It seems as if the idea behind this proposal is to help out database folks. If so, that is misguided. POST is a better implementation than QUERY (or GET) at least for SQL databases. Here's why.

In SQL this is a query:

  SELECT a, b, c FROM foo LIMIT 1

But this is also a "query" in many if not most connectivity APIs.

  INSERT INTO foo VALUES (1, 2, 3)

Most client libraries don't know and don't care about the content of the query. It's the database's job to parse it and and do the right thing. The different between the above queries is that the first one returns a result set and the second returns an update count. Here's a simple example using Python and the clickhouse-driver library.

  # An UPDATE to the database
  client.execute('INSERT INTO iris SELECT * FROM another_iris_table')

  # A harmless "query"
  result = client.execute('SELECT COUNT(*) FROM iris') 
  print(result)

For this to work you need to use something underneath that is generic and works regardless of output. POST does this already. The clickhouse-driver does not use HTTP protocol though other ClickHouse drivers do. I'm just using it as example of why you need a protocol than can handle any type of SQL "query" the same way on the wire. Otherwise the client will have to have a SQL parser to figure out which one to use. (Some clients actually do that but they are a very small minority.)