没有关键参数，视图可以正常工作
$curl "http://127.0.0.1:5984/music/_design/albums/_view/by_release_date"
{"total_rows":311,"offset":0,"rows":[
{"id":"a4327d0718d3b1e227df7124a99a7fc3","key":"1991-12-22","value":{"by":"张楚","title":"黑月亮"}},
{"id":"a4327d0718d3b1e227df7124a99a3ac5","key":"unknown","value":{"by":"郑钧","title":"郑钧:赤裸裸"}},
但是当使用密钥时，我得到的要么是错误的请求响应，要么是空的结果。为什么？
$curl "http://127.0.0.1:5984/music/_design/albums/_view/by_release_date?key=unknown"{“错误”：“bad_request”，“原因”：“invalid_json”}
$curl "http://127.0.0.1:5984/music/_design/albums/_view/by_release_date?key=1993"{“total_rows”：311，“offset”：0，“rows”：[
]}
地图函数为：
map
function(doc) {
key = doc.release_date
value = {by: doc.author , title: doc.title}
emit(key, value);
}
