Add test for HISTOGRAM aggregate

h2/src/test/org/h2/test/scripts/TestScript.java

@@ -162,7 +162,7 @@ public class TestScript extends TestDb {
             testScript("other/" + s + ".sql");
         }
         for (String s : new String[] { "array-agg", "avg", "bit-and", "bit-or", "count", "envelope",
-                "group-concat", "max", "median", "min", "mode", "selectivity", "stddev-pop",
+                "group-concat", "histogram", "max", "median", "min", "mode", "selectivity", "stddev-pop",
                 "stddev-samp", "sum", "var-pop", "var-samp" }) {
             testScript("functions/aggregate/" + s + ".sql");
         }

h2/src/test/org/h2/test/scripts/functions/aggregate/histogram.sql

+-- Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
+-- and the EPL 1.0 (http://h2database.com/html/license.html).
+-- Initial Developer: H2 Group
+--
+
+SELECT HISTOGRAM(X), HISTOGRAM(DISTINCT X) FROM VALUES (1), (2), (3), (1), (2), (NULL), (5) T(X);
+> HISTOGRAM(C1)                               HISTOGRAM(DISTINCT C1)
+> ------------------------------------------- -------------------------------------------
+> ((null, 1), (1, 2), (2, 2), (3, 1), (5, 1)) ((null, 1), (1, 1), (2, 1), (3, 1), (5, 1))
+> rows: 1
+
+SELECT HISTOGRAM(X) FILTER (WHERE X > 1), HISTOGRAM(DISTINCT X) FILTER (WHERE X > 1)
+    FROM VALUES (1), (2), (3), (1), (2), (NULL), (5) T(X);
+> HISTOGRAM(C1) FILTER (WHERE (C1 > 1)) HISTOGRAM(DISTINCT C1) FILTER (WHERE (C1 > 1))
+> ------------------------------------- ----------------------------------------------
+> ((2, 2), (3, 1), (5, 1))              ((2, 1), (3, 1), (5, 1))
+> rows: 1
+
+SELECT HISTOGRAM(X) FILTER (WHERE X > 0), HISTOGRAM(DISTINCT X) FILTER (WHERE X > 0)  FROM VALUES (0) T(X);
+> HISTOGRAM(C1) FILTER (WHERE (C1 > 0)) HISTOGRAM(DISTINCT C1) FILTER (WHERE (C1 > 0))
+> ------------------------------------- ----------------------------------------------
+> ()                                    ()
+> rows: 1