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  • 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。

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  • 原文地址:https://www.cnblogs.com/caohaifeng/p/5550744.html
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