From 1cdf22374be6a23f026cfedd4d099b06f84a301c Mon Sep 17 00:00:00 2001
From: Alexander Barkov <bar@mariadb.com>
Date: Sat, 4 May 2024 22:34:14 +0400
Subject: [PATCH] MDEV-34069 Zero datetime reinterprets as '1970-01-01
 00:00:00' on field_datetime=field_timestamp

The code in Field_timestamp::save_in_field() did not catch
zero datetime and stored it to the other field like a usual value
using store_timestamp_dec(), which knows nothing about zero date and
treats {tv_sec=0, tv_usec=0} as a normal timeval value corresponding to
'1970-01-01 00:00:00 +00:00'.

Fixing the code to catch the special combination (ts==0 && sec_pat==0) and
store it using store_time_dec() with a zero datetime passed as an argument.
---
 mysql-test/main/type_timestamp.result | 30 +++++++++++++++++++++++++++
 mysql-test/main/type_timestamp.test   | 20 ++++++++++++++++++
 sql/field.cc                          |  2 ++
 3 files changed, 52 insertions(+)

diff --git a/mysql-test/main/type_timestamp.result b/mysql-test/main/type_timestamp.result
index f95a1d6ae39..2763b25f58c 100644
--- a/mysql-test/main/type_timestamp.result
+++ b/mysql-test/main/type_timestamp.result
@@ -1368,5 +1368,35 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
 drop table t1;
 #
+# MDEV-34069 Zero datetime reinterprets as '1970-01-01 00:00:00' on field_datetime=field_timestamp
+#
+SET sql_mode='';
+SET time_zone='+00:00';
+CREATE TABLE t1 (a TIMESTAMP);
+INSERT INTO t1 VALUES ('0000-00-00 00:00:00');
+SELECT * FROM t1;
+a
+0000-00-00 00:00:00
+CREATE TABLE t2 (a DATETIME);
+INSERT INTO t2 SELECT a FROM t1;
+SELECT * FROM t2;
+a
+0000-00-00 00:00:00
+SET sql_mode='NO_ZERO_DATE,NO_ZERO_IN_DATE';
+INSERT INTO t2 VALUES ('0000-00-00 00:00:00');
+Warnings:
+Warning	1264	Out of range value for column 'a' at row 1
+INSERT INTO t2 SELECT a FROM t1;
+Warnings:
+Warning	1264	Out of range value for column 'a' at row 1
+SELECT * FROM t2;
+a
+0000-00-00 00:00:00
+0000-00-00 00:00:00
+0000-00-00 00:00:00
+DROP TABLE t2, t1;
+SET time_zone=DEFAULT;
+SET sql_mode=DEFAULT;
+#
 # End of 10.5 tests
 #
diff --git a/mysql-test/main/type_timestamp.test b/mysql-test/main/type_timestamp.test
index 526a0e69857..076ecbd41ed 100644
--- a/mysql-test/main/type_timestamp.test
+++ b/mysql-test/main/type_timestamp.test
@@ -920,6 +920,26 @@ create table t1 (f1 timestamp, f2 timestamp);
 show create table t1;
 drop table t1;
 
+--echo #
+--echo # MDEV-34069 Zero datetime reinterprets as '1970-01-01 00:00:00' on field_datetime=field_timestamp
+--echo #
+
+SET sql_mode='';
+SET time_zone='+00:00';
+CREATE TABLE t1 (a TIMESTAMP);
+INSERT INTO t1 VALUES ('0000-00-00 00:00:00');
+SELECT * FROM t1;
+CREATE TABLE t2 (a DATETIME);
+INSERT INTO t2 SELECT a FROM t1;
+SELECT * FROM t2;
+SET sql_mode='NO_ZERO_DATE,NO_ZERO_IN_DATE';
+INSERT INTO t2 VALUES ('0000-00-00 00:00:00');
+INSERT INTO t2 SELECT a FROM t1;
+SELECT * FROM t2;
+DROP TABLE t2, t1;
+SET time_zone=DEFAULT;
+SET sql_mode=DEFAULT;
+
 --echo #
 --echo # End of 10.5 tests
 --echo #
diff --git a/sql/field.cc b/sql/field.cc
index 828687aeaf3..e428f38b896 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -5184,6 +5184,8 @@ int Field_timestamp::save_in_field(Field *to)
 {
   ulong sec_part;
   my_time_t ts= get_timestamp(&sec_part);
+  if (!ts && !sec_part)
+    return to->store_time_dec(Datetime::zero().get_mysql_time(), decimals());
   return to->store_timestamp_dec(Timeval(ts, sec_part), decimals());
 }