All Implemented Interfaces:
NamedWriteable, Writeable, Resolvable, EvaluatorMapper
Direct Known Subclasses:
Atan2, Case, CIDRMatch, Coalesce, Concat, DateDiff, DateParse, DateTrunc, EndsWith, EsqlConfigurationFunction, FromAggregateMetricDouble, Greatest, Hash, Hypot, In, IpPrefix, Least, Left, Locate, Log, MvAppend, MvPercentile, MvPSeriesWeightedSum, MvSlice, MvSort, MvZip, Pow, Repeat, Replace, Right, Round, StartsWith, Substring, UnaryScalarFunction

public abstract class EsqlScalarFunction extends ScalarFunction implements EvaluatorMapper
A ScalarFunction is a Function that takes values from some operation and converts each to another value. An example would be ABS(), which takes one value at a time, applies a function to the value (abs) and returns a new value.

We have a guide for writing these in the javadoc for org.elasticsearch.xpack.esql.expression.function.scalar.