Implement 'MONTH' in 'DATE_TRUNC'

h2/src/main/org/h2/util/DateTimeFunctions.java

@@ -26,10 +26,8 @@ import static org.h2.expression.Function.WEEK;
 import static org.h2.expression.Function.YEAR;
 
 import java.math.BigDecimal;
-import java.sql.Date;
 import java.text.DateFormatSymbols;
 import java.text.SimpleDateFormat;
-import java.util.Calendar;
 import java.util.GregorianCalendar;
 import java.util.HashMap;
 import java.util.Locale;
@@ -452,6 +450,14 @@ public final class DateTimeFunctions {
             }
             timeNanos = 0l;
             break;
+            
+        case MONTH:
+            
+            long year = DateTimeUtils.yearFromDateValue(dateValue);
+            int month = DateTimeUtils.monthFromDateValue(dateValue);
+            dateValue = DateTimeUtils.dateValue(year, month, 1);
+            timeNanos = 0l;
+            break;
 
         }
         if (timeNanos == null) {

h2/src/test/org/h2/test/scripts/functions/timeanddate/date_trunc.sql

@@ -657,15 +657,73 @@ SELECT DATE_TRUNC('week', '2018-03-14 00:00:00.000');
 >> 2018-03-12 00:00:00
 
 --
--- Test unhandled time unit
+-- Test time unit 'MONTH'
 --
-SELECT DATE_TRUNC('---', '2015-05-29 15:14:13');
-> exception
+select DATE_TRUNC('month', time '00:00:00');
+>> 1970-01-01 00:00:00
+
+select DATE_TRUNC('MONTH', time '00:00:00');
+>> 1970-01-01 00:00:00
+
+select DATE_TRUNC('month', time '15:14:13');
+>> 1970-01-01 00:00:00
+
+select DATE_TRUNC('MONTH', time '15:14:13');
+>> 1970-01-01 00:00:00
+
+select DATE_TRUNC('month', date '2015-05-28');
+>> 2015-05-01 00:00:00
+
+select DATE_TRUNC('MONTH', date '2015-05-28');
+>> 2015-05-01 00:00:00
+
+select DATE_TRUNC('month', timestamp '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00
+
+select DATE_TRUNC('MONTH', timestamp '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00
+
+select DATE_TRUNC('month', timestamp with time zone '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00+00
+
+select DATE_TRUNC('MONTH', timestamp with time zone '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00+00
+
+select DATE_TRUNC('month', timestamp with time zone '2015-05-29 05:14:13-06');
+>> 2015-05-01 00:00:00-06
+
+select DATE_TRUNC('MONTH', timestamp with time zone '2015-05-29 05:14:13-06');
+>> 2015-05-01 00:00:00-06
+
+select DATE_TRUNC('month', timestamp with time zone '2015-05-29 15:14:13+10');
+>> 2015-05-01 00:00:00+10
+
+select DATE_TRUNC('MONTH', timestamp with time zone '2015-05-29 15:14:13+10');
+>> 2015-05-01 00:00:00+10
+
+select DATE_TRUNC('month', '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00
+
+select DATE_TRUNC('MONTH', '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00
+
+SELECT DATE_TRUNC('MONTH', '2018-03-14 00:00:00.000');
+>> 2018-03-01 00:00:00
+
+SELECT DATE_TRUNC('month', '2018-03-14 00:00:00.000');
+>> 2018-03-01 00:00:00
 
 SELECT DATE_TRUNC('month', '2015-05-29 15:14:13');
-> exception
+>> 2015-05-01 00:00:00
 
 SELECT DATE_TRUNC('MONTH', '2015-05-29 15:14:13');
+>> 2015-05-01 00:00:00
+
+
+--
+-- Test unhandled time unit
+--
+SELECT DATE_TRUNC('---', '2015-05-29 15:14:13');
 > exception
 
 SELECT DATE_TRUNC('quarter', '2015-05-29 15:14:13');