聚合框架收集搜索查詢選擇的所有數(shù)據(jù)，并由許多構(gòu)建塊組成，這有助于構(gòu)建數(shù)據(jù)的復(fù)雜摘要。聚合的基本結(jié)構(gòu)如下所示-
"aggregations" : {
"" : {
"" : {
}
[,"meta" : { [] } ]?
[,"aggregations" : { []+ } ]?
}
[,"" : { ... } ]*
}聚合有不同的類型，每種類型都有自己的目的。本章將詳細(xì)討論這些問題。
這些聚合有助于根據(jù)聚合文檔的字段值計(jì)算矩陣，有時還可以從腳本生成一些值。
數(shù)值矩陣既可以是單值（如平均聚合），也可以是多值（如統(tǒng)計(jì)數(shù)據(jù)）。
此聚合用于獲取聚合文檔中存在的任何數(shù)字字段的平均值。例如，
POST /schools/_search
{
"aggs":{
"avg_fees":{"avg":{"field":"fees"}}
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 41,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "schools",
"_type" : "school",
"_id" : "5",
"_score" : 1.0,
"_source" : {
"name" : "Central School",
"description" : "CBSE Affiliation",
"street" : "Nagan",
"city" : "paprola",
"state" : "HP",
"zip" : "176115",
"location" : [
31.8955385,
76.8380405
],
"fees" : 2200,
"tags" : [
"Senior Secondary",
"beautiful campus"
],
"rating" : "3.3"
}
},
{
"_index" : "schools",
"_type" : "school",
"_id" : "4",
"_score" : 1.0,
"_source" : {
"name" : "City Best School",
"description" : "ICSE",
"street" : "West End",
"city" : "Meerut",
"state" : "UP",
"zip" : "250002",
"location" : [
28.9926174,
77.692485
],
"fees" : 3500,
"tags" : [
"fully computerized"
],
"rating" : "4.5"
}
}
]
},
"aggregations" : {
"avg_fees" : {
"value" : 2850.0
}
}
}此聚合提供了特定字段的不同值的計(jì)數(shù)。
POST /schools/_search?size=0
{
"aggs":{
"distinct_name_count":{"cardinality":{"field":"fees"}}
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 2,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"distinct_name_count" : {
"value" : 2
}
}
}Note ?基數(shù)的值為2，因?yàn)橘M(fèi)用有兩個不同的值。
此聚合將生成有關(guān)聚合文檔中特定數(shù)字字段的所有統(tǒng)計(jì)信息。
POST /schools/_search?size=0
{
"aggs" : {
"fees_stats" : { "extended_stats" : { "field" : "fees" } }
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 8,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"fees_stats" : {
"count" : 2,
"min" : 2200.0,
"max" : 3500.0,
"avg" : 2850.0,
"sum" : 5700.0,
"sum_of_squares" : 1.709E7,
"variance" : 422500.0,
"std_deviation" : 650.0,
"std_deviation_bounds" : {
"upper" : 4150.0,
"lower" : 1550.0
}
}
}
}此聚合查找聚合文檔中特定數(shù)字字段的最大值。
POST /schools/_search?size=0
{
"aggs" : {
"max_fees" : { "max" : { "field" : "fees" } }
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 16,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"max_fees" : {
"value" : 3500.0
}
}
}此聚合在聚合的文檔中查找特定數(shù)字字段的最小值。
POST /schools/_search?size=0
{
"aggs" : {
"min_fees" : { "min" : { "field" : "fees" } }
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 2,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"min_fees" : {
"value" : 2200.0
}
}
}此聚合計(jì)算聚合文檔中特定數(shù)值字段的和。
POST /schools/_search?size=0
{
"aggs" : {
"total_fees" : { "sum" : { "field" : "fees" } }
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 8,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"total_fees" : {
"value" : 5700.0
}
}
}在特殊情況下還有其他一些度量標(biāo)準(zhǔn)聚合，例如地理邊界聚合和地理質(zhì)心聚合，以實(shí)現(xiàn)地理位置。
一種多值度量標(biāo)準(zhǔn)聚合，可根據(jù)從聚合文檔中提取的數(shù)值來計(jì)算統(tǒng)計(jì)信息。
POST /schools/_search?size=0
{
"aggs" : {
"grades_stats" : { "stats" : { "field" : "fees" } }
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 2,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"grades_stats" : {
"count" : 2,
"min" : 2200.0,
"max" : 3500.0,
"avg" : 2850.0,
"sum" : 5700.0
}
}
}您可以在請求時使用meta標(biāo)記添加一些有關(guān)聚合的數(shù)據(jù)，并作為響應(yīng)獲取。
POST /schools/_search?size=0
{
"aggs" : {
"min_fees" : { "avg" : { "field" : "fees" } ,
"meta" :{
"dsc" :"Lowest Fees This Year"
}
}
}
}在運(yùn)行上面的代碼時，我們得到以下結(jié)果-
{
"took" : 0,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : null,
"hits" : [ ]
},
"aggregations" : {
"min_fees" : {
"meta" : {
"dsc" : "Lowest Fees This Year"
},
"value" : 2850.0
}
}
}