# Joining multiple document within same index with joining the key
**URL:** https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680
**Category:** Elasticsearch
**Tags:** eql-elastic-query-language
**Created:** [August 27, 2021, 2:45pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680 "2021-08-27T14:45:21Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Cap\_Ho](https://discuss.elastic.co/u/Cap_Ho)
#### Post date: [August 27, 2021, 2:45pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680/1 "2021-08-27T14:45:21Z")
Just have an question on query to join multiple document together.
For example , i have the following 6 document into same index:
{
"\_id" : 1,
"studentId" : "a11",
"class" : "1A",
"classNumber" : 11
},
{
"\_id" : 2,
"studentId" : "a11",
"hobby" :"swimming"
},
{
"\_id" : 3,
"studentId" : "a11",
"Country" : "USA"
},
{
"\_id" : 4,
"studentId" : "b22",
"class" : "1B",
"classNumber" : 50
},
{
"\_id" : 5,
"studentId" : "b22",
"hobby" :"cooking"
},
{
"\_id" : 6,
"studentId" : "c33",
"Country" : "USA"
}
May i know if i may use DSL query to join the document together based on a key (e.g. "studentId") and become like this?
{
"\_id" : 1,
"studentId" : "a11",
"class" : "1A",
"classNumber" : 11
"hobby" :"swimming"
"Country" : "USA"
},
{
"\_id" : 4,
"studentId" : "b22",
"class" : "1B",
"classNumber" : 50
"hobby" :"cooking"
},
{
"\_id" : 6,
"studentId" : "c33",
"Country" : "USA"
}
Or i need to create a new index? Any other suggestion are welcome.
---
### Author:  [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)
#### Post date: [August 27, 2021, 3:00pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680/2 "2021-08-27T15:00:13Z")
Elasticsearch does not support joins so I would recommend indexed by the data as you want to retrieve and query it.
---
### Author:  [@Cap\_Ho](https://discuss.elastic.co/u/Cap_Ho)
#### Post date: [August 27, 2021, 3:17pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680/3 "2021-08-27T15:17:05Z")
what you mean is prepare the data first (deformalized it first) and put in index?
---
### Author:  [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)
#### Post date: [August 27, 2021, 3:17pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680/4 "2021-08-27T15:17:44Z")
Yes.
---
### Author:  [@Cap\_Ho](https://discuss.elastic.co/u/Cap_Ho)
#### Post date: [August 27, 2021, 3:40pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680/5 "2021-08-27T15:40:17Z")
But sometime we cannot deformalize it from the beginning . (e.g. they are insert in different timestamp by restful API). So in this case we need to and another layer to join it first before put in index? No other choice?
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [September 24, 2021, 3:40pm UTC](https://discuss.elastic.co/t/joining-multiple-document-within-same-index-with-joining-the-key/282680/6 "2021-09-24T15:40:54Z")
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