Added min function for string field and fixed query 29 in tests

integ-test/src/test/resources/clickbench/queries/q29.ppl

@@ -4,9 +4,9 @@ AVG(length(Referer)) AS l, COUNT(*) AS c, MIN(Referer)
 FROM hits WHERE Referer <> '' GROUP BY k HAVING COUNT(*) > 100000 ORDER BY l DESC LIMIT 25;
 */
 source=hits
-| Referer != ''
-| eval k = regexp_replace(Referer, '^https?://(?:www\.)?([^/]+)/.*$', '\1')
-| stats bucket_nullable=false avg(length(Referer)) as l, count() as c, min(Referer) by k
-| where c > 1
+| where Referer != ''
+| eval k = replace(Referer, '^https?://(?:www\\.)?([^/]+)/.*$', '\\1')
+| stats avg(length(Referer)) as l, count() as c, min(Referer) by k
+| where c > 100000
 | sort - l
 | head 25

opensearch/src/main/java/org/opensearch/sql/opensearch/request/OpenSearchQueryRequest.java

@@ -482,6 +482,7 @@ public static byte[] convertToSubstraitAndSerialize(RelNode relNode) {
     private static SubstraitRelVisitor createVisitor(RelNode relNode) {
       //Mapping of Function names in Calcite to Substrait
         List<FunctionMappings.Sig> customSigs = List.of(
+                new FunctionMappings.Sig(SqlStdOperatorTable.MIN, "min"),
                 new FunctionMappings.Sig(PPLBuiltinOperators.EXTRACT, "date_part"),
                 new FunctionMappings.Sig(PPLBuiltinOperators.STRFTIME, "date_format"),
                 new FunctionMappings.Sig(PPLBuiltinOperators.DATE_FORMAT, "date_format"),

opensearch/src/main/resources/opensearch_custom_functions.yaml

@@ -21,3 +21,11 @@ scalar_functions:
             value: precision_timestamp<P>
         return: i64
 
+aggregate_functions:
+  - name: min
+    description: Find the minimum value of a string
+    impls:
+      - args:
+          - name: x
+            value: string
+        return: i64