MongoDB干貨篇之查詢數(shù)據(jù)
在開(kāi)始之前我們應(yīng)該先準(zhǔn)備數(shù)據(jù)方便演示，這里我插入的了幾條數(shù)據(jù)，數(shù)據(jù)如下：
- db.user.insertMany(
- [{
- name:'jack',
- age:22,
- sex:'Man',
- tags:['python','c++','c'],
- grades:[22,33,44,55],
- school:{
- name:'shida',
- city:'xuzhou'
- }
- },{
- name:'jhon',
- age:33,
- sex:null,
- tags:['python','java'],
- grades:[66,22,44,88],
- school:{
- name:'kuangda',
- city:'xuzhou'
- }
- },
- {
- name:'xiaoming',
- age:33,
- tags:['python','java'],
- grades:[66,22,44,88],
- school:{
- name:'kuangda',
- city:'xuzhou'
- }
- }
- ]
- )
find( , )
其中 query 表示查找的條件，相當(dāng)于 mysql 中 where 子句, projection 列出你想要查找的數(shù)據(jù)，格式為 db.collection.find(find(<query filter>, <projection>))
實(shí)例：
下面不帶參數(shù)的查找，將會(huì)查找出所有的結(jié)果
- db.find().pretty();
- //輸出結(jié)果
- {
- "_id" : ObjectId("59056f81299fe049404b2899"),
- "name" : "jack",
- "age" : 22,
- "tags" : [
- "python",
- "c++",
- "c"
- ],
- "grades" : [
- 22,
- 33,
- 44,
- 55
- ],
- "school" : {
- "name" : "shida",
- "city" : "xuzhou"
- }
- }
下面找出滿足 name 為 jack 的數(shù)據(jù)，并且只輸出 name , age ,這里的 _id 是默認(rèn)輸出的，如果不想輸出將將它設(shè)置為 0 ，想要輸出那個(gè)字段將它設(shè)置為1
- db.user.find({name:'jack'},{name:1,age:1})
- //輸出結(jié)果
- { "_id" : ObjectId("59056f81299fe049404b2899"), "name" : "jack", "age" : 22 }
- db.user.find({name:'jack'},{name:1,age:1，_id:0})
- //輸出結(jié)果
- {"name" : "jack", "age" : 22 }
**注意這里的一個(gè) projection 不能 同時(shí) 指定包括和排除字段，除了排除 _id 字段。 在 顯式包括 字段的映射中， _id 字段是***一個(gè)您可以 顯式排除 的。
查詢內(nèi)嵌文檔
上述例子中插入的 school 數(shù)據(jù)就表示內(nèi)嵌文檔
完全匹配查詢
完全匹配查詢表示 school 中的查詢數(shù)組必須和插入的數(shù)組完全一樣，順序都必須一樣才能查找出來(lái)
- db.user.find({name:'jack',school:{name:'shida',city:'xuzhou'}});
- //輸出結(jié)果
- { "_id" : ObjectId("59056f81299fe049404b2899"), "name" : "jack", "age" : 22, "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
- //下面是指定輸出的字段，這里的school.name表示只輸出school文檔中name字段，必須加引號(hào)
- db.user.find({name:'jack',school:{name:'shida',city:'xuzhou'}},{name:1,age:1,'school.name':1});
- //輸出結(jié)果
- { "_id" : ObjectId("59056f81299fe049404b2899"), "name" : "jack", "age" : 22, "school" : { "name" : "shida" } }
鍵值對(duì)查詢
可以通過(guò)鍵值對(duì)查詢，不用考慮順序，比如 'school.name':'shida' ，表示查詢學(xué)校名字為shida 的數(shù)據(jù)，這里的引號(hào)是必須要的
- db.user.find({'school.name':'shida'},{name:1,school:1});
- //輸出結(jié)果
- { "_id" : ObjectId("59056f81299fe049404b2899"), "name" : "jack", "school" : { "name" : "shida", "city" : "xuzhou" } }
查詢操作符
下面我們將配合查詢操作符來(lái)執(zhí)行復(fù)雜的查詢操作，比如元素查詢、 邏輯查詢 、比較查詢操作。我們使用下面的比較操作符 "$gt" 、 "$gte" 、 "$lt" 、 "$lte" (分別對(duì)應(yīng) ">" 、 ">=" 、 "<" 、 "<=" )
實(shí)例
下面查詢年齡在 20-30 之間的信息
- db.user.find({
- age:{$gt:20,$lt:30}
- })
- //輸出
- { "_id" : ObjectId("59056f81299fe049404b2899"), "name" : "jack", "age" : 22, "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
$ne
$ne 表示不相等，例如查詢年齡不等于 22 歲的信息
- db.user.find({age:{$ne:22}})
- //輸出
- { "_id" : ObjectId("59057c16f551d8c9003d31e0"), "name" : "jhon", "age" : 33, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
slice
$slice 操作符控制查詢返回的數(shù)組中元素的個(gè)數(shù)。此操作符根據(jù)參數(shù) { field: value } 指定鍵名和鍵值選擇出文檔集合，并且該文檔集合中指定 array 鍵將返回從指定數(shù)量的元素。如果 count 的值大于數(shù)組中元素的數(shù)量，該查詢返回?cái)?shù)組中的所有元素的。
語(yǔ)法： db.collection.find( { field: value }, { array: {$slice: count }}) ;
下面將查詢 grades 中的前兩個(gè)數(shù)
- db.user.find({name:'jack'},{grades:{$slice:2},name:1,age:1,'school.name':1});
- //輸出，可以看出這里的grades只輸出了前面兩個(gè)
- { "_id" : ObjectId("59057c16f551d8c9003d31df"), "name" : "jack", "age" : 22, "grades" : [ 22, 33 ], "school" : { "name" : "shida" } }
下面將輸出后3個(gè)數(shù)據(jù)
- db.user.find({name:'jhon'},{grades:{$slice:-3},name:1});
- //輸出
- { "_id" : ObjectId("59057c16f551d8c9003d31e0"), "name" : "jhon", "grades" : [ 22, 44, 88 ] }
下面介紹指定一個(gè)數(shù)組作為參數(shù)。數(shù)組參數(shù)使用 [ skip , limit ] 格式，其中***個(gè)值表示在數(shù)組中跳過(guò)的項(xiàng)目數(shù),第二個(gè)值表示返回的項(xiàng)目數(shù)。
- db.user.find({name:'jack'},{grades:{$slice:[2,2]},name:1}); //這里將會(huì)跳過(guò)前面的兩個(gè)，直接得到后面的兩個(gè)數(shù)據(jù)
- //輸出
- { "_id" : ObjectId("59057c16f551d8c9003d31df"), "name" : "jack", "grades" : [ 44, 55 ] }
$exists
如果 $exists 的值為 true ,選擇存在該字段的文檔,若值為 false 則選擇不包含該字段的文檔
下面將會(huì)查詢不存在sex這一項(xiàng)的信息
- db.user.find({sex:{$exists:false}})
- //結(jié)果
- { "_id" : ObjectId("59058460fe58ed1089f2a5cd"), "name" : "xiaoming", "age" : 33, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
- db.user.find({sex:{$exists:true}});
- //結(jié)果
- { "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
- { "_id" : ObjectId("59058460fe58ed1089f2a5cc"), "name" : "jhon", "age" : 33, "sex" : null, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
$or
執(zhí)行邏輯 OR 運(yùn)算,指定一個(gè)至少包含兩個(gè)表達(dá)式的數(shù)組，選擇出至少滿足數(shù)組中一條表達(dá)式的文檔。
語(yǔ)法： { $or: [ { <expression1> }, { <expression2> }, ... , { <expressionN> } ] }
下面將要查找 age 等于 22 或者 age 等于 33 的值
- db.user.find({$or:[{age:22},{age:33}]})
- //結(jié)果
- { "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
- { "_id" : ObjectId("59058460fe58ed1089f2a5cc"), "name" : "jhon", "age" : 33, "sex" : null, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
- { "_id" : ObjectId("59058460fe58ed1089f2a5cd"), "name" : "xiaoming", "age" : 33, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
下面將會(huì)查找出年齡為22或者33并且姓名為 jack 的人的信息
- db.user.find({name:'jack',$or:[{age:33},{age:22}]})
- //結(jié)果
- { "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
$and
指定一個(gè)至少包含兩個(gè)表達(dá)式的數(shù)組，選擇出滿足該數(shù)組中所有表達(dá)式的文檔。 $and 操作符使用短路操作，若***個(gè)表達(dá)式的值為“ false ”,余下的表達(dá)式將不會(huì)執(zhí)行。
語(yǔ)法： { $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }
下面將會(huì)查找年齡在 20-30 之間的信息，對(duì)于下面使用逗號(hào)分隔符的表達(dá)式列表， MongoDB會(huì)提供一個(gè)隱式的 $and 操作：
- db.user.find({$and:[{age:{$gt:20}},{age:{$lt:30}}]})
- //上述語(yǔ)句相當(dāng)于db.user.find({age:{$gt:20},age:{$lt:30}})
- //結(jié)果
- { "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
$in
匹配鍵值等于指定數(shù)組中任意值的文檔。類似 sql 中 in ，只要匹配一個(gè) value 就會(huì)輸出
語(yǔ)法： { field: { $in: [<value1>, <value2>, ... <valueN> ] } }
下面將會(huì)查找grades中存在22,33之間的任意一個(gè)數(shù)的信息
- db.user.find({grades:{$in:[22,33]}})
- //輸出
- { "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
- { "_id" : ObjectId("59058460fe58ed1089f2a5cc"), "name" : "jhon", "age" : 33, "sex" : null, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
- { "_id" : ObjectId("59058460fe58ed1089f2a5cd"), "name" : "xiaoming", "age" : 33, "tags" : [ "python", "java" ],
- "grades" : [ 66, 22, 44, 88 ], "school" : { "name" : "kuangda", "city" : "xuzhou" } }
$nin
匹配鍵不存在或者鍵值不等于指定數(shù)組的任意值的文檔。類似 sql 中 not in (SQL中字段不存在使用會(huì)有語(yǔ)法錯(cuò)誤).
查詢出 grades 中不存在100或者44的文檔
- db.user.find({grades:{$nin:[100,44]}})
$not
執(zhí)行邏輯 NOT 運(yùn)算，選擇出不能匹配表達(dá)式的文檔 ，包括沒(méi)有指定鍵的文檔。 $not 操作符不能獨(dú)立使用，必須跟其他操作一起使用
語(yǔ)法:{ field: { $not: { } } }
查詢年齡不大于30的信息
- db.user.find({age:{$not:{$gt:30}}})
- //輸出
- { "_id" : ObjectId("59058460fe58ed1089f2a5cb"), "name" : "jack", "age" : 22, "sex" : "Man", "tags" : [ "python", "c++", "c" ],
- "grades" : [ 22, 33, 44, 55 ], "school" : { "name" : "shida", "city" : "xuzhou" } }
