title: Apache Calcite: Convert a SQL parse tree into a tree of relational expressions WITHOUT validation
body: <p>I'm currently working on a project in which I want to parse an SQL-Query and create the tree of relational expressions for it.
  The main goal is to identify the join partners in the Queries.
  So I'd like to push the join-expressions down to the leafs of the tree.
  To achieve this, I decided to use Apache Calcite.
  My code looks roughly like this at the moment:</p>
  
  <pre><code>Planner planner = Frameworks.getPlanner(Frameworks.newConfigBuilder().defaultSchema(Frameworks.createRootSchema(false)).build());
  
  SqlNode parsed = planner.parse("SELECT s.dnasamplename, e.Total_expression_level, e.Soluble_expression_level, s.id " +
              "FROM table1 e" +
              "JOIN table2 s on s.constructname = e.Clone_name" +
              "WHERE e.Total_expression_level like '0:%'");
  
  planner.validate(parsed);
  
  RelRoot relRoot = planner.rel(parsed);
  </code></pre>
  
  <p>If I try to execute the rel-Method of <a href="https://calcite.apache.org/apidocs/org/apache/calcite/tools/Planner.html" rel="nofollow noreferrer">Planner</a> directly, I get the error that I have to validate the query first. And that`s the point where I face troubles. I don't have a valid Schema. I just want to convert the query to a relational query plan. Is there a way to kind of skip the validation process?</p>