Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 2)
     Function count (children 1)
      ExpressionList
     Function toString (children 1)
      ExpressionList (children 1)
       Identifier json.a
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier test
    ExpressionList (children 1)
     Function toString (children 1)
      ExpressionList (children 1)
       Identifier json.a
    Set
