Fix for Bug#11326.

mysql-test/r/date_formats.result:
  Added test cases for Bug#11326
mysql-test/t/date_formats.test:
  Added test cases for Bug#11326

mysql-test/r/date_formats.result

@@ -473,3 +473,21 @@ NULL
 select str_to_date( 1, IF(1=1,NULL,NULL) );
 str_to_date( 1, IF(1=1,NULL,NULL) )
 NULL
+SELECT TIME_FORMAT("24:00:00", '%r');
+TIME_FORMAT("24:00:00", '%r')
+12:00:00 AM
+SELECT TIME_FORMAT("00:00:00", '%r');
+TIME_FORMAT("00:00:00", '%r')
+12:00:00 AM
+SELECT TIME_FORMAT("12:00:00", '%r');
+TIME_FORMAT("12:00:00", '%r')
+12:00:00 PM
+SELECT TIME_FORMAT("15:00:00", '%r');
+TIME_FORMAT("15:00:00", '%r')
+03:00:00 PM
+SELECT TIME_FORMAT("01:00:00", '%r');
+TIME_FORMAT("01:00:00", '%r')
+01:00:00 AM
+SELECT TIME_FORMAT("25:00:00", '%r');
+TIME_FORMAT("25:00:00", '%r')
+01:00:00 AM

mysql-test/t/date_formats.test

@@ -276,3 +276,14 @@ select str_to_date( 1, NULL );
 select str_to_date( NULL, 1 );
 select str_to_date( 1, IF(1=1,NULL,NULL) );
 # End of 4.1 tests
+
+#
+# Bug#11326
+#
+
+SELECT TIME_FORMAT("24:00:00", '%r');
+SELECT TIME_FORMAT("00:00:00", '%r');
+SELECT TIME_FORMAT("12:00:00", '%r');
+SELECT TIME_FORMAT("15:00:00", '%r');
+SELECT TIME_FORMAT("01:00:00", '%r');
+SELECT TIME_FORMAT("25:00:00", '%r');

sql/item_timefunc.cc

@@ -620,7 +620,8 @@ bool make_date_time(DATE_TIME_FORMAT *format, TIME *l_time,
       case 'r':
 	length= my_sprintf(intbuff, 
 		   (intbuff, 
-		    (l_time->hour < 12) ? "%02d:%02d:%02d AM" : "%02d:%02d:%02d PM",
+		    ((l_time->hour % 24) < 12) ?
+                    "%02d:%02d:%02d AM" : "%02d:%02d:%02d PM",
 		    (l_time->hour+11)%12+1,
 		    l_time->minute,
 		    l_time->second));