Explain EXPLAIN SYNTAX (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 1)
    ExpressionList (children 1)
     Function equals (children 1)
      ExpressionList (children 2)
       Function isNull (children 1)
        ExpressionList (children 1)
         Literal UInt64_1
       Literal UInt64_0