Correct DATEADD description in help.csv

h2/src/docsrc/help/help.csv

@@ -3668,12 +3668,15 @@ CURRENT_TIMESTAMP()
 "Functions (Time and Date)","DATEADD","
 { DATEADD| TIMESTAMPADD } (unitString, addIntLong, timestamp)
 ","
-Adds units to a timestamp. The string indicates the unit.
+Adds units to a date-time value. The string indicates the unit.
 Use negative values to subtract units.
 addIntLong may be a long value when manipulating milliseconds,
 otherwise it's range is restricted to int.
 The same units as in the EXTRACT function are supported.
-DATEADD method returns a timestamp. TIMESTAMPADD method returns a long.
+DATEADD method returns a value with the same type as specified value if unit is compatible with this value.
+If specified unit is a HOUR, MINUTE, SECOND, MILLISECOND, etc and value is a DATE value DATEADD returns combined TIMESTAMP.
+Units DAY, MONTH, YEAR, WEEK, etc are not allowed for TIME values.
+TIMESTAMPADD method returns a long.
 ","
 DATEADD('MONTH', 1, DATE '2001-01-31')
 "

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

@@ -1817,7 +1817,7 @@ public class Function extends Expression implements FunctionCall {
         case YEAR:
         case MONTH: {
             if (!withDate) {
-                throw DbException.getInvalidValueException("DATEADD timestamp", v);
+                throw DbException.getInvalidValueException("DATEADD time part", part);
             }
             long year = DateTimeUtils.yearFromDateValue(dateValue);
             long month = DateTimeUtils.monthFromDateValue(dateValue);
@@ -1838,7 +1838,7 @@ public class Function extends Expression implements FunctionCall {
         case DAY_OF_MONTH:
         case DAY_OF_YEAR:
             if (!withDate) {
-                throw DbException.getInvalidValueException("DATEADD timestamp", v);
+                throw DbException.getInvalidValueException("DATEADD time part", part);
             }
             dateValue = DateTimeUtils.dateValueFromAbsoluteDay(
                     DateTimeUtils.absoluteDayFromDateValue(dateValue) + count);