Manual merge of fix for bugs of #7297 and #7515 into 4.1 tree.

mysql-test/r/func_time.result

@@ -474,12 +474,15 @@ unix_timestamp(@a)
 select unix_timestamp('1969-12-01 19:00:01');
 unix_timestamp('1969-12-01 19:00:01')
 0
-select from_unixtime(0);
-from_unixtime(0)
+select from_unixtime(-1);
+from_unixtime(-1)
 NULL
 select from_unixtime(2145916800);
 from_unixtime(2145916800)
 NULL
+select from_unixtime(0);
+from_unixtime(0)
+1970-01-01 03:00:00
 CREATE TABLE t1 (datetime datetime, timestamp timestamp, date date, time time);
 INSERT INTO t1 values ("2001-01-02 03:04:05", "2002-01-02 03:04:05", "2003-01-02", "06:07:08");
 SELECT * from t1;

mysql-test/r/type_datetime.result

@@ -143,3 +143,13 @@ t
 0000-00-00 00:00:00
 2003-01-01 00:00:00
 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/func_time.test

@@ -231,10 +231,14 @@ select unix_timestamp('1969-12-01 19:00:01');
 
 #
 # Test for bug #6439 "unix_timestamp() function returns wrong datetime 
-# values for too big argument". It should return error instead.
+# values for too big argument" and bug #7515 "from_unixtime(0) now
+# returns NULL instead of the epoch". unix_timestamp() should return error
+# for too big or negative argument. It should return Epoch value for zero
+# argument since it seems that many user's rely on this fact.
 #
-select from_unixtime(0);
+select from_unixtime(-1);
 select from_unixtime(2145916800);
+select from_unixtime(0);
 
 #
 # Test types from + INTERVAL

mysql-test/t/type_datetime.test

@@ -89,3 +89,15 @@ delete from t1;
 insert into t1 values ("0000-00-00 00:00:00 some trailer"),("2003-01-01 00:00:00 some trailer");
 select * from t1;
 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/item_timefunc.cc

@@ -1636,11 +1636,12 @@ longlong Item_func_from_unixtime::val_int()
 bool Item_func_from_unixtime::get_date(TIME *ltime,
 				       uint fuzzy_date __attribute__((unused)))
 {
-  longlong tmp= args[0]->val_int();
-
-  if ((null_value= (args[0]->null_value ||
-                    tmp < TIMESTAMP_MIN_VALUE ||
-                    tmp > TIMESTAMP_MAX_VALUE)))
+  ulonglong tmp= (ulonglong)(args[0]->val_int());
+  /*
+    "tmp > TIMESTAMP_MAX_VALUE" check also covers case of negative
+    from_unixtime() argument since tmp is unsigned.
+  */
+  if ((null_value= (args[0]->null_value || tmp > TIMESTAMP_MAX_VALUE)))
     return 1;
 
   thd->variables.time_zone->gmt_sec_to_TIME(ltime, (my_time_t)tmp);