db.users.ensureIndex({age:1})

db.t3.ensureIndex({age:1} , {backgroud:true})

db.factories.insert( { name: "wwl", addr: { city: "Beijing", state: "BJ" } } );//在addr 列上創建索引db.factories.ensureIndex( { addr : 1 } );//下面這個查詢將會用到我們剛剛建立的索引db.factories.find( { addr: { city: "Beijing", state: "BJ" } } );//但是下面這個查詢將不會用到索引，因為查詢的順序跟索引建立的順序不一樣db.factories.find( { addr: { state: "BJ" , city: "Beijing"} } );

db.factories.ensureIndex( { "addr.city" : 1, "addr.state" : 1 } );// 下面的查詢都用到了這個索引db.factories.find( { "addr.city" : "Beijing", "addr.state" : "BJ" } );db.factories.find( { "addr.city" : "Beijing" } );db.factories.find().sort( { "addr.city" : 1, "addr.state" : 1 } );db.factories.find().sort( { "addr.city" : 1 } )

db.t4.ensureIndex({firstname: 1, lastname: 1}, {unique: true});

db.t5.find({age:{$lt:30}}).hint({name:1, age:1}).explain()

//刪除t3 表中的所有索引db.t3.dropIndexes()//刪除t4 表中的firstname 索引db.t4.dropIndex({firstname: 1})

db.t5.ensureIndex({name:1}) db.t5.ensureIndex({age:1}) db.t5.find({age:{$gt:45}}, {name:1}).explain() {   "cursor" : "BtreeCursor age_1",   "nscanned" : 0,   "nscannedObjects" : 0,   "n" : 0,   "millis" : 0,   "nYields" : 0,   "nChunkSkips" : 0,   "isMultiKey" : false,   "indexOnly" : false,   "indexBounds" : {   "age" : [          [45,1.7976931348623157e+308]        ]    }}