# multi_match 的 most_fiels 策略
- most-fiels: 在多个 field 查询到关键词的则优先返回该 doc
- best_fields：在一个 field 中匹配到多个查询词的则优先返回该 doc
他们两个是刚好相反的一个策略
现在来实验，首先添加测试数据
POST /forum/article/_bulk
{ "update": { "_id": "1"} }
{ "doc" : {"sub_title" : "learning more courses"} }
{ "update": { "_id": "2"} }
{ "doc" : {"sub_title" : "learned a lot of course"} }
{ "update": { "_id": "3"} }
{ "doc" : {"sub_title" : "we have a lot of fun"} }
{ "update": { "_id": "4"} }
{ "doc" : {"sub_title" : "both of them are good"} }
{ "update": { "_id": "5"} }
{ "doc" : {"sub_title" : "haha, hello world"} }
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GET /forum/article/_search
{
"query": {
"match": {
"sub_title": "learning courses"
}
}
}
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这个查询出来的结果我们希望是 id=1 的数据会排在最前面，因为最相关。但是使用默认的 mapping 就不一定
原理就是：sub_title 会自动 mapping 成 enligsh analyzer，所以还原了单词
为什么，因为如果我们用的是类似于 english analyzer 这种分词器的话，就会将单词还原为其最基本的形态（stemmer）
learning --> learn
learned --> learn
courses --> course
sub_titile: learning coureses --> learn course
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这样转换后再查询，相关分就和我们想象的不太一样了。所以先处理该差异，手动 mapping
POST /forum/_mapping/article
{
"properties": {
"sub_title": {
"type": "string",
"analyzer": "english",
"fields": {
"std": {
"type": "string",
"analyzer": "standard"
}
}
}
}
}
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再次查询
GET /forum/article/_search
{
"query": {
"match": {
"sub_title.std": "learning courses"
}
}
}
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就只会返回一条了，因为只有这一条符合标准
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0.5063205,
"hits": [
{
"_index": "forum",
"_type": "article",
"_id": "1",
"_score": 0.5063205,
"_source": {
"articleID": "XHDK-A-1293-#fJ3",
"userID": 1,
"hidden": false,
"postDate": "2017-01-01",
"tag": [
"java",
"hadoop"
],
"tag_cnt": 2,
"view_cnt": 30,
"title": "this is java and elasticsearch blog",
"content": "i like to write best elasticsearch article",
"sub_title": "learning more courses"
}
}
]
}
}
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如果不使用 .std 就会使用分词形式去匹配到两条数据。multi_match 语法如下
GET /forum/article/_search
{
"query": {
"multi_match": {
"query": "learning courses",
"type": "most_fields",
"fields": [ "sub_title", "sub_title.std" ]
}
}
}
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响应结果
{
"took": 3,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 2,
"max_score": 1.219939,
"hits": [
{
"_index": "forum",
"_type": "article",
"_id": "2",
"_score": 1.219939,
"_source": {
"articleID": "KDKE-B-9947-#kL5",
"userID": 1,
"hidden": false,
"postDate": "2017-01-02",
"tag": [
"java"
],
"tag_cnt": 1,
"view_cnt": 50,
"title": "this is java blog",
"content": "i think java is the best programming language",
"sub_title": "learned a lot of course"
}
},
{
"_index": "forum",
"_type": "article",
"_id": "1",
"_score": 1.012641,
"_source": {
"articleID": "XHDK-A-1293-#fJ3",
"userID": 1,
"hidden": false,
"postDate": "2017-01-01",
"tag": [
"java",
"hadoop"
],
"tag_cnt": 2,
"view_cnt": 30,
"title": "this is java and elasticsearch blog",
"content": "i like to write best elasticsearch article",
"sub_title": "learning more courses"
}
}
]
}
}
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但是这还是没有出现我们希望的结果是为什么呢？这个老师也讲解不清楚了，计算很复杂；但是有一点可以知道， 使用 best_fields 和 most_fields 查看对于 id=1 的评分， 在 most_fields 策略下 评分达到了 1+ ，而 best_fields 策略下只有 0.5+；
这就可以说明 most_fields 策略的作用了
GET /forum/article/_search
{
"query": {
"multi_match": {
"query": "learning courses",
"type": "best_fields",
"fields": [ "sub_title", "sub_title.std" ]
}
}
}
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