ES|QL multivalued fields
ES|QL is fine reading from multivalued fields:
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:
{
"took": 28,
"is_partial": false,
"columns": [
{ "name": "a", "type": "long"},
{ "name": "b", "type": "long"}
],
"values": [
[1, [1, 2]],
[2, 3]
]
}
The relative order of values in a multivalued field is undefined. They’ll frequently be in ascending order but don’t rely on that.
Some field types, like keyword remove duplicate values on write:
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 ES|QL sees that removal:
{
"took": 28,
"is_partial": false,
"columns": [
{ "name": "a", "type": "long"},
{ "name": "b", "type": "keyword"}
],
"values": [
[1, ["bar", "foo"]],
[2, "bar"]
]
}
But other types, like long don’t remove duplicates.
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 ES|QL also sees that:
{
"took": 28,
"is_partial": false,
"columns": [
{ "name": "a", "type": "long"},
{ "name": "b", "type": "long"}
],
"values": [
[1, [1, 2, 2]],
[2, [1, 1]]
]
}
This is all at the storage layer. If you store duplicate longs and then convert them to strings the duplicates will stay:
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"
}
{
"took": 28,
"is_partial": false,
"columns": [
{ "name": "a", "type": "long"},
{ "name": "b", "type": "keyword"}
],
"values": [
[1, ["1", "2", "2"]],
[2, ["1", "1"]]
]
}
null values in a list are not preserved at the storage layer:
POST /mv/_doc?refresh { "a": [2, null, 1] }
POST /_query
{
"query": "FROM mv | LIMIT 1"
}
{
"took": 28,
"is_partial": false,
"columns": [
{ "name": "a", "type": "long"},
],
"values": [
[[1, 2]],
]
}
Unless otherwise documented functions will return null when applied to a multivalued field.
POST /mv/_bulk?refresh { "index" : {} }
{ "a": 1, "b": [2, 1] }
{ "index" : {} }
{ "a": 2, "b": 3 }
POST /_query {
"query": "FROM mv | EVAL b + 2, a + b | LIMIT 4"
}
{
"took": 28,
"is_partial": false,
"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]
]
}
Work around this limitation by converting the field to single value with one of:
POST /_query {
"query": "FROM mv | EVAL b=MV_MIN(b) | EVAL b + 2, a + b | LIMIT 4"
}
{
"took": 28,
"is_partial": false,
"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]
]
}