MongoDB小结17

我们再添加一个游泳的人，并用$in查询游泳的人

db.user.find({"hobby":{"$in":["swimming"]}},{"_id":0})
{ "hobby" : "swimming", "gender" : "female" }
{ "hobby" : "swimming", "gender" : "male" }

$in 是对单个键进行的查询，用$or查询可以匹配多个键

db.user.find({"$or":[{"hobby":"swimming"},{"gender":"female"}]},{"_id":0})
{ "hobby" : "swimming", "gender" : "female" }
{ "hobby" : "swimming", "gender" : "male" } 

现在，我们把查询条件的female改成male

db.user.find({"$or":[{"hobby":"swimming"},{"gender":"male"}]},{"_id":0})
{ "hobby" : "swimming", "gender" : "female" }
{ "hobby" : "dancing", "gender" : "male" }
{ "hobby" : "singing", "gender" : "male" }
{ "hobby" : "singing", "gender" : "male" }
{ "hobby" : "dancing", "gender" : "male" }
{ "hobby" : "swimming", "gender" : "male" }

现在我们可以得出结论，OR查询（$in 和 $or）是尽可能的获取更多的匹配项。 OR查询其实是取并集，满足其中一条及以上，即可被查询到。