Changing hybrid search section, adding info about aggregations

Signed-off-by: Martin Gaievski <[email protected]>

_search-plugins/hybrid-search.md

@@ -24,6 +24,7 @@ To use hybrid search, follow these steps:
 1. [Ingest documents into the index](#step-3-ingest-documents-into-the-index).
 1. [Configure a search pipeline](#step-4-configure-a-search-pipeline).
 1. [Search the index using hybrid search](#step-5-search-the-index-using-hybrid-search).
+1. [Enhance results of hybrid search](#step-6-enhance-results-of-hybrid-search).
 
 ## Step 1: Create an ingest pipeline
 
@@ -216,3 +217,198 @@ The response contains the matching document:
   }
 }
 ```
+
+## Step 6: Enhance results of hybrid search
+
+You cam combine hybrid query clause with other OpenSearch query features to enhance search expirience. Following existing clauses can be used together with hybrid query:
+ - Aggregations
+
+### Aggregations
+Aggreations allow you to use OpenSearch as analytics engine. For more detailed information about aggregations, see [`Aggregations`]({{site.url}}{{site.baseurl}}/aggregations/).
+
+Hybrid query can be combined with any aggregation that is supported by OpenSearch. Aggregation performed on sub-set of documents that is returned by hybrid query, except for [`global`]({{site.url}}{{site.baseurl}}/aggregations/bucket/global)
+aggreagtion that is done for all documents.
+
+To illustrate how aggreagtions can be used with hybrid query first let's create index. Aggreagtions typically used with a special field types, like `keyword` or `integer`. Following example will create index with fields of these types:
+
+```json
+PUT /my-nlp-index
+{
+    "settings": {
+        "number_of_shards": 2
+    },
+    "mappings": {
+        "properties": {
+            "doc_index": {
+                "type": "integer"
+            },
+            "doc_keyword": {
+                "type": "keyword"
+            },
+            "category": {
+                "type": "keyword"
+            }
+        }
+    }
+}
+```
+
+Following requests will ingest 6 documents to our new index:
+
+```json
+POST /_bulk
+{ "index": { "_index": "my-nlp-index" } }
+{ "category": "permission", "doc_keyword": "workable", "doc_index": 4976, "doc_price": 100}
+{ "index": { "_index": "my-nlp-index" } }
+{ "category": "sister", "doc_keyword": "angry", "doc_index": 2231, "doc_price": 200 }
+{ "index": { "_index": "my-nlp-index" } }
+{ "category": "hair", "doc_keyword": "likeable", "doc_price": 25 }
+{ "index": { "_index": "my-nlp-index" } }
+{ "category": "editor", "doc_index": 9871, "doc_price": 30 }
+{ "index": { "_index": "my-nlp-index" } }
+{ "category": "statement", "doc_keyword": "entire", "doc_index": 8242, "doc_price": 350  } 
+{ "index": { "_index": "my-nlp-index" } }
+{ "category": "statement", "doc_keyword": "idea", "doc_index": 5212, "doc_price": 200  } 
+{ "index": { "_index": "index-test" } }
+{ "category": "editor", "doc_keyword": "bubble", "doc_index": 1298, "doc_price": 130 } 
+{ "index": { "_index": "index-test" } }
+{ "category": "editor", "doc_keyword": "bubble", "doc_index": 521, "doc_price": 75  } 
+```
+
+
+The following example request combines hybrid query with min aggregation:
+
+```json
+GET /my-nlp-index/_search?search_pipeline=nlp-search-pipeline
+{
+    "query": {
+        "hybrid": {
+            "queries": [
+                {
+                    "term": {
+                        "category": "permission"
+                    }
+                },
+                {
+                    "bool": {
+                        "should": [
+                            {
+                                "term": {
+                                    "category": "editor"
+                                }
+                            },
+                            {
+                                "term": {
+                                    "category": "statement"
+                                }
+                            }
+                        ]
+                    }
+                }
+            ]
+        }
+    },
+    "aggs": {
+        "total_price": {
+            "sum": {
+                "field": "doc_price"
+            }
+        },
+        "keywords": {
+            "terms": {
+                "field": "doc_keyword",
+                "size": 10
+            }
+        }
+    }
+}
+```
+
+The response contains the matching document and results of aggregations: 
+```json
+{
+    "took": 9,
+    "timed_out": false,
+    "_shards": {
+        "total": 2,
+        "successful": 2,
+        "skipped": 0,
+        "failed": 0
+    },
+    "hits": {
+        "total": {
+            "value": 4,
+            "relation": "eq"
+        },
+        "max_score": 0.5,
+        "hits": [
+            {
+                "_index": "my-nlp-index",
+                "_id": "mHRPNY4BlN82W_Ar9UMY",
+                "_score": 0.5,
+                "_source": {
+                    "doc_price": 100,
+                    "doc_index": 4976,
+                    "doc_keyword": "workable",
+                    "category": "permission"
+                }
+            },
+            {
+                "_index": "my-nlp-index",
+                "_id": "m3RPNY4BlN82W_Ar9UMY",
+                "_score": 0.5,
+                "_source": {
+                    "doc_price": 30,
+                    "doc_index": 9871,
+                    "category": "editor"
+                }
+            },
+            {
+                "_index": "my-nlp-index",
+                "_id": "nXRPNY4BlN82W_Ar9UMY",
+                "_score": 0.5,
+                "_source": {
+                    "doc_price": 200,
+                    "doc_index": 5212,
+                    "doc_keyword": "idea",
+                    "category": "statement"
+                }
+            },
+            {
+                "_index": "my-nlp-index",
+                "_id": "nHRPNY4BlN82W_Ar9UMY",
+                "_score": 0.5,
+                "_source": {
+                    "doc_price": 350,
+                    "doc_index": 8242,
+                    "doc_keyword": "entire",
+                    "category": "statement"
+                }
+            }
+        ]
+    },
+    "aggregations": {
+        "total_price": {
+            "value": 680.0
+        },
+        "doc_keywords": {
+            "doc_count_error_upper_bound": 0,
+            "sum_other_doc_count": 0,
+            "buckets": [
+                {
+                    "key": "entire",
+                    "doc_count": 1
+                },
+                {
+                    "key": "idea",
+                    "doc_count": 1
+                },
+                {
+                    "key": "workable",
+                    "doc_count": 1
+                }
+            ]
+        }
+    }
+}
+```