elasticsearch/docs/reference/esql/implicit-casting.asciidoc

[[esql-implicit-casting]]
=== {esql} implicit casting

++++
<titleabbrev>Implicit casting</titleabbrev>
++++

Often users will input `date`, `ip`, `version`, `date_period` or `time_duration` as simple strings in their queries for use in predicates, functions, or expressions. {esql} provides <<esql-type-conversion-functions, type conversion functions>> to explicitly convert these strings into the desired data types.

Without implicit casting users must explicitly code these `to_X` functions in their queries, when string literals don't match the target data types they are assigned or compared to. Here is an example of using `to_datetime` to explicitly perform a data type conversion.

[source.merge.styled,esql]
----
FROM employees
| EVAL dd_ns1=date_diff("day", to_datetime("2023-12-02T11:00:00.00Z"), birth_date)
| SORT emp_no
| KEEP dd_ns1
| LIMIT 1
----

Implicit casting improves usability, by automatically converting string literals to the target data type. This is most useful when the target data type is `date`, `ip`, `version`, `date_period` or `time_duration`. It is natural to specify these as a string in queries.

The first query can be coded without calling the `to_datetime` function, as follows:

[source.merge.styled,esql]
----
FROM employees
| EVAL dd_ns1=date_diff("day", "2023-12-02T11:00:00.00Z", birth_date)
| SORT emp_no
| KEEP dd_ns1
| LIMIT 1
----

[float]
=== Implicit casting support

The following table details which {esql} operations support implicit casting for different data types.

[%header.monospaced.styled,format=dsv,separator=|]
|===
||ScalarFunction*|Operator*|<<esql-group-functions, GroupingFunction>>|<<esql-agg-functions, AggregateFunction>>
|DATE|Y|Y|Y|N
|IP|Y|Y|Y|N
|VERSION|Y|Y|Y|N
|BOOLEAN|Y|Y|Y|N
|DATE_PERIOD/TIME_DURATION|Y|N|Y|N
|===

ScalarFunction* includes:

<<esql-conditional-functions-and-expressions, Conditional Functions and Expressions>>

<<esql-date-time-functions, Date and Time Functions>>

<<esql-ip-functions, IP Functions>>


Operator* includes:

<<esql-binary-operators, Binary Operators>>

<<esql-unary-operators, Unary Operator>>

<<esql-in-operator, IN>>