elasticsearch/docs/reference/esql/multivalued-fields.asciidoc

[[esql-multivalued-fields]]
=== {esql} multivalued fields

++++
<titleabbrev>Multivalued fields</titleabbrev>
++++

{esql} is fine reading from multivalued fields:

[source,console,id=esql-multivalued-fields-reorders]
----
POST /mv/_bulk?refresh
{ "index" : {} }
{ "a": 1, "b": [2, 1] }
{ "index" : {} }
{ "a": 2, "b": 3 }

POST /_query
{
  "query": "FROM mv | LIMIT 2"
}
----

Multivalued fields come back as a JSON array:

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a", "type": "long"},
    { "name": "b", "type": "long"}
  ],
  "values": [
    [1, [1, 2]],
    [2,      3]
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]


The relative order of values in a multivalued field is undefined. They'll frequently be in
ascending order but don't rely on that.

[discrete]
[[esql-multivalued-fields-dups]]
==== Duplicate values

Some field types, like <<keyword-field-type,`keyword`>> remove duplicate values on write:

[source,console,id=esql-multivalued-fields-kwdups]
----
PUT /mv
{
  "mappings": {
    "properties": {
      "b": {"type": "keyword"}
    }
  }
}

POST /mv/_bulk?refresh
{ "index" : {} }
{ "a": 1, "b": ["foo", "foo", "bar"] }
{ "index" : {} }
{ "a": 2, "b": ["bar", "bar"] }

POST /_query
{
  "query": "FROM mv | LIMIT 2"
}
----

And {esql} sees that removal:

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a", "type": "long"},
    { "name": "b", "type": "keyword"}
  ],
  "values": [
    [1, ["bar", "foo"]],
    [2,          "bar"]
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]


But other types, like `long` don't remove duplicates.

[source,console,id=esql-multivalued-fields-longdups]
----
PUT /mv
{
  "mappings": {
    "properties": {
      "b": {"type": "long"}
    }
  }
}

POST /mv/_bulk?refresh
{ "index" : {} }
{ "a": 1, "b": [2, 2, 1] }
{ "index" : {} }
{ "a": 2, "b": [1, 1] }

POST /_query
{
  "query": "FROM mv | LIMIT 2"
}
----

And {esql} also sees that:

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a", "type": "long"},
    { "name": "b", "type": "long"}
  ],
  "values": [
    [1, [1, 2, 2]],
    [2,    [1, 1]]
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]


This is all at the storage layer. If you store duplicate `long`s and then
convert them to strings the duplicates will stay:

[source,console,id=esql-multivalued-fields-longdups-tostring]
----
PUT /mv
{
  "mappings": {
    "properties": {
      "b": {"type": "long"}
    }
  }
}

POST /mv/_bulk?refresh
{ "index" : {} }
{ "a": 1, "b": [2, 2, 1] }
{ "index" : {} }
{ "a": 2, "b": [1, 1] }

POST /_query
{
  "query": "FROM mv | EVAL b=TO_STRING(b) | LIMIT 2"
}
----

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a", "type": "long"},
    { "name": "b", "type": "keyword"}
  ],
  "values": [
    [1, ["1", "2", "2"]],
    [2,      ["1", "1"]]
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]

[discrete]
[[esql-multivalued-nulls]]
==== `null` in a list

`null` values in a list are not preserved at the storage layer:

[source,console,id=esql-multivalued-fields-multivalued-nulls]
----
POST /mv/_doc?refresh
{ "a": [2, null, 1] }

POST /_query
{
  "query": "FROM mv | LIMIT 1"
}
----

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a", "type": "long"},
  ],
  "values": [
    [[1, 2]],
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]

[discrete]
[[esql-multivalued-fields-functions]]
==== Functions

Unless otherwise documented functions will return `null` when applied to a multivalued
field.

[source,console,id=esql-multivalued-fields-mv-into-null]
----
POST /mv/_bulk?refresh
{ "index" : {} }
{ "a": 1, "b": [2, 1] }
{ "index" : {} }
{ "a": 2, "b": 3 }
----

[source,console]
----
POST /_query
{
  "query": "FROM mv | EVAL b + 2, a + b | LIMIT 4"
}
----
// TEST[continued]
// TEST[warning:Line 1:16: evaluation of [b + 2] failed, treating result as null. Only first 20 failures recorded.]
// TEST[warning:Line 1:16: java.lang.IllegalArgumentException: single-value function encountered multi-value]
// TEST[warning:Line 1:23: evaluation of [a + b] failed, treating result as null. Only first 20 failures recorded.]
// TEST[warning:Line 1:23: java.lang.IllegalArgumentException: single-value function encountered multi-value]

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a",   "type": "long"},
    { "name": "b",   "type": "long"},
    { "name": "b + 2", "type": "long"},
    { "name": "a + b", "type": "long"}
  ],
  "values": [
    [1, [1, 2], null, null],
    [2,      3,    5,    5]
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]

Work around this limitation by converting the field to single value with one of:

* <<esql-mv_avg>>
* <<esql-mv_concat>>
* <<esql-mv_count>>
* <<esql-mv_max>>
* <<esql-mv_median>>
* <<esql-mv_min>>
* <<esql-mv_sum>>

[source,console,esql-multivalued-fields-mv-into-null]
----
POST /_query
{
  "query": "FROM mv | EVAL b=MV_MIN(b) | EVAL b + 2, a + b | LIMIT 4"
}
----
// TEST[continued]

[source,console-result]
----
{
  "took": 28,
  "columns": [
    { "name": "a",   "type": "long"},
    { "name": "b",   "type": "long"},
    { "name": "b + 2", "type": "long"},
    { "name": "a + b", "type": "long"}
  ],
  "values": [
    [1, 1, 3, 2],
    [2, 3, 5, 5]
  ]
}
----
// TESTRESPONSE[s/"took": 28/"took": "$body.took"/]