SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 2)
    Function JSONExtract (alias x) (children 1)
     ExpressionList (children 2)
      Literal \'{"a":1, "b":"test"}\'
      Literal \'Tuple(a UInt8, b String)\'
    Identifier x.a
   Set
