deplace all the code logic into a function

h2/src/main/org/h2/expression/Function.java

@@ -1496,23 +1496,11 @@ public class Function extends Expression implements FunctionCall {
             result = ValueLong.get(datediff(v0.getString(), v1, v2));
             break;
         case DATE_TRUNC:
-            // Retrieve the field value (e.g. 'day', 'microseconds', etc.)
-            String fieldValue = StringUtils.toUpperEnglish(v0.getString());
+            // Retrieve the time unit (e.g. 'day', 'microseconds', etc.)
+            String timeUnit = StringUtils.toUpperEnglish(v0.getString());
 
-            // Retrieve the dateValue.
-            long[] fieldDateAndTime = DateTimeUtils.dateAndTimeFromValue(v1);
-            long fieldDateValue = fieldDateAndTime[0];
+            result = DateTimeUtils.truncateDate(timeUnit, v1);
 
-            // Case where the date has to be truncated to the day.
-            if (fieldValue.equals("DAY")) {
-
-                result = DateTimeUtils.truncateToDay(v1, fieldDateValue);
-
-            } else {
-
-                // Return an exception for the other possible value (not yet supported).
-                throw DbException.getUnsupportedException(v0.getString());
-            }
             break;
         case EXTRACT: {
             int field = getDatePart(v0.getString());

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

@@ -1474,28 +1474,42 @@ public class DateTimeUtils {
     /**
      * Truncate the given date to 'day'
      * 
+     * @param timeUnit the time unit (e.g. 'DAY', 'HOUR', etc.)
      * @param value the date
-     * @param dateValue the dateValue used if the value is not a timestamp time
-     *            zone
      * @return date truncated to 'day'
      */
-    public static Value truncateToDay(Value value, long dateValue) {
+    public static Value truncateDate(String timeUnit, Value value) {
         Value result = null;
 
-        if (value instanceof ValueTimestampTimeZone) {
+        // Retrieve the dateValue.
+        long[] fieldDateAndTime = DateTimeUtils.dateAndTimeFromValue(value);
+        long dateValue = fieldDateAndTime[0];
 
-            // Create a new ValueTimestampTimeZone by only setting the
-            // date. The time in nanoseconds since midnight will be set
-            // to 0.
-            ValueTimestampTimeZone vTmp = (ValueTimestampTimeZone) value;
-            result = ValueTimestampTimeZone.fromDateValueAndNanos(vTmp.getDateValue(), 0, vTmp.getTimeZoneOffsetMins());
+        // Case where the date has to be truncated to the day.
+        if (timeUnit.equals("DAY")) {
 
+            if (value instanceof ValueTimestampTimeZone) {
+
+                // Create a new ValueTimestampTimeZone by only setting the
+                // date. The time in nanoseconds since midnight will be set
+                // to 0.
+                ValueTimestampTimeZone vTmp = (ValueTimestampTimeZone) value;
+                result = ValueTimestampTimeZone.fromDateValueAndNanos(vTmp.getDateValue(), 0,
+                        vTmp.getTimeZoneOffsetMins());
+
+            } else {
+
+                // By default, we create a timestamp by setting the
+                // datevalue to the datevalue retrieved and the time in
+                // nanoseconds since midnight to 0.
+                result = ValueTimestamp.fromDateValueAndNanos(dateValue, 0);
+
+            }
         } else {
 
-            // By default, we create a timestamp by setting the
-            // datevalue to the datevalue retrieved and the time in nanoseconds
-            // since midnight to 0.
-            result = ValueTimestamp.fromDateValueAndNanos(dateValue, 0);
+            // Return an exception for the other possible value (not yet
+            // supported).
+            throw DbException.getUnsupportedException(timeUnit);
         }
 
         return result;