SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function map (alias m) (children 1)
     ExpressionList (children 4)
      Literal \'a\'
      Literal UInt64_2
      Literal \'b\'
      Literal NULL
   ExpressionList (children 3)
    Function arrayElement (children 1)
     ExpressionList (children 2)
      Identifier m
      Function toNullable (children 1)
       ExpressionList (children 1)
        Literal \'a\'
    Function arrayElement (children 1)
     ExpressionList (children 2)
      Identifier m
      Function toNullable (children 1)
       ExpressionList (children 1)
        Literal \'b\'
    Function arrayElement (children 1)
     ExpressionList (children 2)
      Identifier m
      Function toNullable (children 1)
       ExpressionList (children 1)
        Literal \'c\'