Explain EXPLAIN (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 1)
     Function hostName (alias hostName) (children 1)
      ExpressionList
    TablesInSelectQuery (children 2)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier system.query_log (alias a)
     TablesInSelectQueryElement (children 2)
      TableExpression (children 1)
       TableIdentifier system.processes (alias b)
      TableJoin (children 1)
       Function and (children 1)
        ExpressionList (children 2)
         Function equals (children 1)
          ExpressionList (children 2)
           Identifier a.query_id
           Identifier b.query_id
         Function equals (children 1)
          ExpressionList (children 2)
           Identifier type
           Literal \'QueryStart\'
    Function equals (children 1)
     ExpressionList (children 2)
      Identifier current_database
      Function currentDatabase (children 1)
       ExpressionList
    Set
