ESQL: Fix Max doubles bug with negatives and add tests for Max and Min

docs/changelog/110586.yaml

@@ -0,0 +1,5 @@
+pr: 110586
+summary: "ESQL: Fix Max doubles bug with negatives and add tests for Max and Min"
+area: ES|QL
+type: bug
+issues: []

docs/reference/esql/functions/aggregation-functions.asciidoc

@@ -11,10 +11,10 @@ The <<esql-stats-by>> command supports these aggregate functions:
 * <<esql-avg>>
 * <<esql-agg-count>>
 * <<esql-agg-count-distinct>>
-* <<esql-agg-max>>
+* <<esql-max>>
 * <<esql-agg-median>>
 * <<esql-agg-median-absolute-deviation>>
-* <<esql-agg-min>>
+* <<esql-min>>
 * <<esql-agg-percentile>>
 * experimental:[] <<esql-agg-st-centroid>>
 * <<esql-agg-sum>>
@@ -25,14 +25,14 @@ The <<esql-stats-by>> command supports these aggregate functions:
 
 include::count.asciidoc[]
 include::count-distinct.asciidoc[]
-include::max.asciidoc[]
 include::median.asciidoc[]
 include::median-absolute-deviation.asciidoc[]
-include::min.asciidoc[]
 include::percentile.asciidoc[]
 include::st_centroid_agg.asciidoc[]
 include::sum.asciidoc[]
 include::layout/avg.asciidoc[]
+include::layout/max.asciidoc[]
+include::layout/min.asciidoc[]
 include::layout/top.asciidoc[]
 include::values.asciidoc[]
 include::weighted-avg.asciidoc[]

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/aggregation/MaxDoubleAggregator.java

@@ -16,7 +16,7 @@
 class MaxDoubleAggregator {
 
     public static double init() {
-        return Double.MIN_VALUE;
+        return -Double.MAX_VALUE;
     }
 
     public static double combine(double current, double v) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/aggregate/Max.java

@@ -18,6 +18,7 @@
 import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.type.DataType;
 import org.elasticsearch.xpack.esql.expression.SurrogateExpression;
+import org.elasticsearch.xpack.esql.expression.function.Example;
 import org.elasticsearch.xpack.esql.expression.function.FunctionInfo;
 import org.elasticsearch.xpack.esql.expression.function.Param;
 import org.elasticsearch.xpack.esql.expression.function.scalar.multivalue.MvMax;
@@ -31,7 +32,16 @@ public class Max extends NumericAggregate implements SurrogateExpression {
     @FunctionInfo(
         returnType = { "double", "integer", "long", "date" },
         description = "The maximum value of a numeric field.",
-        isAggregation = true
+        isAggregation = true,
+        examples = {
+            @Example(file = "stats", tag = "max"),
+            @Example(
+                description = "The expression can use inline functions. For example, to calculate the maximum "
+                    + "over an average of a multivalued column, use `MV_AVG` to first average the "
+                    + "multiple values per row, and use the result with the `MAX` function",
+                file = "stats",
+                tag = "docsStatsMaxNestedExpression"
+            ) }
     )
     public Max(Source source, @Param(name = "number", type = { "double", "integer", "long", "date" }) Expression field) {
         super(source, field);