xQuery变量持有通配符*（任意）

Question

我想为参数化函数的XPATH过滤器，但希望有机会指示我想要所有结果。明显的例子

declare function search-by-author($author as xs:string*) as element()*{ 
    /Data/Books[@autor=$author] 
}; 

search-by-author(()) -> If null no results even if some books did not have @autor attr 
search-by-author('') -> If empty, only shows those books with @author='' 
search-by-author(('a','b')) -> Returns books by authors 'a' or 'b' 
search-by-author(*) -> THIS MY CURRENT PROBLEM. 

我怎么会效仿吗？是否有任何特殊的PARAM或语法传递*作为一个变量，所以我可以做

$var = * --> /Data/Books[@autor=$var] 

或

$var = EMPTY --> /Data/Books[@autor=$var] --> /Data/Books[@autor] 

谢谢！

Answer 1

随着

declare function search-by-author($author as xs:string*) as element()*{ 
    /Data/Books[$author='*' or @autor=$author] 
}; 

你可以做

search-by-author('*')