elasticsearch/docs/reference/esql/functions/mv_first.asciidoc

[discrete]
[[esql-mv_first]]
=== `MV_FIRST`
[.text-center]
image::esql/functions/signature/mv_first.svg[Embedded,opts=inline]

Converts a multivalued field into a single valued field containing the first value. This is most
useful when reading from a function that emits multivalued fields in a known order like <<esql-split>>:

[source.merge.styled,esql]
----
include::{esql-specs}/string.csv-spec[tag=mv_first]
----
[%header.monospaced.styled,format=dsv,separator=|]
|===
include::{esql-specs}/string.csv-spec[tag=mv_first-result]
|===

The order that <<esql-multivalued-fields, multivalued fields>> are read from underlying storage is not
guaranteed. It is *frequently* ascending, but don't rely on that. If you need the minimum field value
use <<esql-mv_min>> instead of `MV_FIRST`. `MV_MIN` has optimizations for sorted values so there isn't
a performance benefit to `MV_FIRST`. `MV_FIRST` is mostly useful with functions that create multivalued
fields like `SPLIT`.

Supported types:

include::types/mv_first.asciidoc[]