MongoDB学习四

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为了提高MongoDB的读取速度，可以通过建立索引来实现读取速度的显著提高，下面是一些MongoDB中对索引的一些操作：

（1）建立索引：

> db.testnum.ensureIndex({"name":1});{        "createdCollectionAutomatically" : false,        "numIndexesBefore" : 1,        "numIndexesAfter" : 2,        "ok" : 1}>>> db.testnum.ensureIndex({"name":-1});{        "createdCollectionAutomatically" : false,        "numIndexesBefore" : 2,        "numIndexesAfter" : 3,        "ok" : 1}>>> db.testnum.getIndexes();[        {                "v" : 1,                "key" : {                        "_id" : 1                },                "name" : "_id_",                "ns" : "test.testnum"        },        {                "v" : 1,                "key" : {                        "name" : 1                },                "name" : "name_1",                "ns" : "test.testnum"        },        {                "v" : 1,                "key" : {                        "name" : -1                },                "name" : "name_-1",                "ns" : "test.testnum"        }]>>>

”1“和”-1“分别代表按照升序和降序来进行索引。

（2）建立联合索引：

> db.testnum.ensureIndex({"name":1,"age":1});{        "createdCollectionAutomatically" : false,        "numIndexesBefore" : 3,        "numIndexesAfter" : 4,        "ok" : 1}>

（3）删除索引：

> db.testnum.dropIndex({"name":1});{ "nIndexesWas" : 4, "ok" : 1 }>>> db.testnum.getIndexes();[        {                "v" : 1,                "key" : {                        "_id" : 1                },                "name" : "_id_",                "ns" : "test.testnum"        },        {                "v" : 1,                "key" : {                        "name" : -1                },                "name" : "name_-1",                "ns" : "test.testnum"        },        {                "v" : 1,                "key" : {                        "name" : 1,                        "age" : 1                },                "name" : "name_1_age_1",                "ns" : "test.testnum"        }]>

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