SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 3)
    Identifier key
    Identifier s1.value
    Identifier s2.value
   TablesInSelectQuery (children 2)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      Subquery (alias s1) (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 1)
         SelectQuery (children 1)
          ExpressionList (children 2)
           Literal \'key1\' (alias key)
           Literal \'value1\' (alias value)
    TablesInSelectQueryElement (children 2)
     TableExpression (children 1)
      Subquery (alias s2) (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 2)
         SelectQuery (children 1)
          ExpressionList (children 2)
           Literal \'key1\' (alias key)
           Literal \'\' (alias value)
         SelectQuery (children 1)
          ExpressionList (children 2)
           Literal \'key2\' (alias key)
           Function toNullable (alias value) (children 1)
            ExpressionList (children 1)
             Literal \'\'
     TableJoin (children 1)
      ExpressionList (children 1)
       Identifier key
