【文章內(nèi)容簡(jiǎn)介】 b668711a),x:6,name:caihuafeng4} {_id:ObjectId(4bee804ba23d558eb668711b),x:6,name:caihuafeng5} {_id:ObjectId(4bee804ba23d558eb668711c),x:6,name:caihuafeng6} {_id:ObjectId(4bee804ba23d558eb668711d),x:6,name:caihuafeng7} {_id:ObjectId(4bee804ba23d558eb668711e),x:6,name:caihuafeng8} {_id:ObjectId(4bee804ba23d558eb668711f),x:6,name:caihuafeng9} {_id:ObjectId(4bee804ba23d558eb6687120),x:6,name:caihuafeng10}()顯示出來(lái)的一共有2個(gè)索引，其中_id是創(chuàng)建表的時(shí)候自動(dòng)創(chuàng)建的索引，此索引是不能夠刪除的。An index is always created on _id. This index is special and cannot be deleted. The _id index enforces uniqueness for its keys.MongoDB的官方文檔上面是這樣說(shuō)的:Documents as KeysIndexed fields may be of any type, including documents:往數(shù)據(jù)庫(kù)remender的表data中插入三條記錄1. ({name:1616,info:{url:,city:beijing}})。 2. ({name:hao123,info:{url:,city:beijing}})。 3. ({name:ll4la,info:{url:,city:dongguan}})。對(duì)字段info創(chuàng)建索引1. ({info:1})。顯示表data上的所有索引1. ()。 2. [ 3. { 4. name:_id_, 5. ns:, 6. key:{ 7. _id:1 8. } 9. }, 10. { 11. _id:ObjectId(4befb146b0e29ba1ce20e0bb), 12. ns:, 13. key:{ 14. x:1 15. }, 16. name:x_1 17. }, 18. { 19. _id:ObjectId(4befb76bb0e29ba1ce20e0bf), 20. ns:, 21. key:{ 22. info:1 23. }, 24. name:info_1 25. } 26. ]查找指定的記錄，此時(shí)會(huì)用到索引({info:{url:,city:beijing}})。 {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}}建立組合索引({:1,:1})。 ()。 [ { name:_id_, ns:, key:{ _id:1 } }, { _id:ObjectId(4befb146b0e29ba1ce20e0bb), ns:, key:{ x:1 }, name:x_1 }, { _id:ObjectId(4befb76bb0e29ba1ce20e0bf), ns:, key:{ info:1 }, name:info_1 }, { _id:ObjectId(4befb9d1b0e29ba1ce20e0c0), ns:, key:{ :1, :1 }, name: } ]下面幾個(gè)操作均會(huì)用到索引({:,:beijing})。 {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}} ({:})。 {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}}1表示升序(asc)，1表示降序(desc)({:/:*/i}).sort({:1,:1})。 {_id:ObjectId(4befb740b0e29ba1ce20e0be),name:ll4la,info:{url:,city:dongguan}} {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}} {_id:ObjectId(4befb723b0e29ba1ce20e0bd),name:hao123,info:{url:,city:beijing}} ({:/:*/i}).sort({:1})。 {_id:ObjectId(4befb740b0e29ba1ce20e0be),name:ll4la,info:{url:,city:dongguan}} {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}} {_id:ObjectId(4befb723b0e29ba1ce20e0bd),name:hao123,info:{url:,city:beijing}} ({:/:*/i}).sort({:1})。 {_id:ObjectId(4befb723b0e29ba1ce20e0bd),name:hao123,info:{url:,city:beijing}} {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}} {_id:ObjectId(4befb740b0e29ba1ce20e0be),name:ll4la,info:{url:,city:dongguan}}注意，這里的組合索引與上述3中的b中的組合索引是有點(diǎn)不同的，4里面是對(duì)一級(jí)字段建立組合索引，而上述3中是對(duì)二級(jí)字段建立組合索引。在字段name及info上面創(chuàng)建組合索引({name:1,info:1})。 當(dāng)創(chuàng)建組合索引時(shí)，字段后面的1表示升序，1表示降序，是用1還是用1主要是跟排序的時(shí)候或指定范圍內(nèi)查詢的時(shí)候有關(guān)的，具體看下面的英文原文的說(shuō)明。When creating an index, the number associated with a key specifies the direction of the index, so it should always be 1 (ascending) or 1 (descending). Direction doesn’t matter for single key indexes or for random access retrieval but is important if you are doing sorts or range queries on pound indexes.顯示所有的索引1. ()。 2. [ 3. { 4. name:_id_, 5. ns:, 6. key:{ 7. _id:1 8. } 9. }, 10. { 11. _id:ObjectId(4befb146b0e29ba1ce20e0bb), 12. ns:, 13. key:{ 14. x:1 15. }, 16. name:x_1 17. }, 18. { 19. _id:ObjectId(4befb76bb0e29ba1ce20e0bf), 20. ns:, 21. key:{ 22. info:1 23. }, 24. name:info_1 25. }, 26. { 27. _id:ObjectId(4befb9d1b0e29ba1ce20e0c0), 28. ns:, 29. key:{ 30. :1, 31. :1 32. }, 33. name: 34. }, 35. { 36. _id:ObjectId(4befbfcfb0e29ba1ce20e0c1), 37. ns:, 38. key:{ 39. name:1, 40. info:1 41. }, 42. name:name_1_info_1 43. } 44. ]下面的排序?qū)⒂玫缴厦娴乃饕詈笠恍械摹皀ame” : “l(fā)l4la”實(shí)際上是”name” : “114la”(就是將數(shù)字一寫成了字母l)，但是我錄入的時(shí)候?qū)懗闪恕皀ame” : “l(fā)l4la”，是我寫錯(cuò)了，但是排序的結(jié)果是對(duì)的。({:/:*/i}).sort({name:1,info:1})。 {_id:ObjectId(4befb711b0e29ba1ce20e0bc),name:1616,info:{url:,city:beijing}} {_id:ObjectId(4befb723b0e29ba1ce20e0bd),name:hao123,info:{url:,city:beijing}} {_id:ObjectId(4befb740b0e29ba1ce20e0be),name:ll4la,info:{url:,city:dongguan}}MongoDB組合索