Fix for bug #7297 "Two digit year should be interpreted correctly

even with zero month and day" aka "Date decoding trouble"

Two digit year should be interpreted correctly as year in 20th or 21st
century even with zero month and day. Only exception should be zero date
'00-00-00' or '00-00-00 00:00:00'.

mysql-test/r/type_datetime.result

@@ -102,3 +102,13 @@ insert into t1 values (now(), now());
 select * from t1 where a is null or b is null;
 a	b
 drop table t1;
+create table t1 (dt datetime);
+insert into t1 values ("12-00-00"), ("00-00-00 01:00:00");
+insert into t1 values ("00-00-00"), ("00-00-00 00:00:00");
+select * from t1;
+dt
+2012-00-00 00:00:00
+2000-00-00 01:00:00
+0000-00-00 00:00:00
+0000-00-00 00:00:00
+drop table t1;

mysql-test/t/type_datetime.test

@@ -68,3 +68,15 @@ insert into t1 values (now(), now());
 insert into t1 values (now(), now());
 select * from t1 where a is null or b is null;
 drop table t1;
+
+#
+# Test for bug #7297 "Two digit year should be interpreted correctly even
+# with zero month and day"
+#
+create table t1 (dt datetime);
+# These dates should be treated as dates in 21st century
+insert into t1 values ("12-00-00"), ("00-00-00 01:00:00");
+# Zero dates are still special :/
+insert into t1 values ("00-00-00"), ("00-00-00 00:00:00");
+select * from t1;
+drop table t1;

sql/time.cc

@@ -410,7 +410,7 @@ str_to_TIME(const char *str, uint length, TIME *l_time,bool fuzzy_date)
   else
     date[6]=0;
 
-  if (year_length == 2 && i >=2 && (date[1] || date[2]))
+  if (year_length == 2 && not_zero_date)
     date[0]+= (date[0] < YY_PART_YEAR ? 2000 : 1900);
   number_of_fields=i;
   while (i < 6)