A simple CRUD API can be written as given below, noting that the database url should be customised to match your setup.

from quart import g, Quart, request
from quart_db import QuartDB

app = Quart(__name__)
db = QuartDB(app, url="postgresql://username:password@")

async def get_all():
    results = await g.connection.fetch_all("SELECT col1, col2 FROM tbl")
    return [{"a": row["col1"], "b": row["col2"]} for row in results]

async def create():
    data = await request.get_json()
    await g.connection.execute(
        "INSERT INTO tbl (col1, col2) VALUES (:col1, :col2)",
        {"col1": data["a"], "col2": data["b"]},
    return {}

async def get(id):
    result = await g.connection.fetch_one(
        "SELECT col1, col2 FROM tbl WHERE id = :id",
        {"id": id},
    return {"a": result["col1"], "b": result["col2"]}

async def delete(id):
    await g.connection.execute("DELETE FROM tbl WHERE id = :id", {"id": id})
    return {}

async def update(id):
    data = await request.get_json()
    await g.connection.execute(
        "UPDATE tbl SET col1 = :col1, col2 = :col2 WHERE id = :id",
        {"id": id, "col1": data["a"], "col2": data["b"]},
    return {}