text: --
  --    Copyright 2010-2020 the original author or authors.
  --
  --    Licensed under the Apache License, Version 2.0 (the "License");
  --    you may not use this file except in compliance with the License.
  --    You may obtain a copy of the License at
  --
  --       http://www.apache.org/licenses/LICENSE-2.0
  --
  --    Unless required by applicable law or agreed to in writing, software
  --    distributed under the License is distributed on an "AS IS" BASIS,
  --    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  --    See the License for the specific language governing permissions and
  --    limitations under the License.
  --
  
  drop table parent if exists;
  drop table child if exists;
  drop table pet if exists;
  
  create table parent (
  id int,
  col1 varchar(20),
  col2 varchar(20)
  );
  
  create table child (
  id int,
  parent_id int,
  name varchar(20)
  );
  
  create table pet (
  id int,
  parent_id int,
  name varchar(20)
  );
  
  insert into parent (id, col1, col2) values
  (1, null, null),
  (2, null, null);
  
  insert into child (id, parent_id, name) values
  (1, 2, 'john'),
  (2, 2, 'mary');
  