We're converting from MySQL 5.1 to MariaDB 5.5.44 and I'm hoping someone can help clarify for me what's going on in the following scenario. In brief, we're getting milliseconds displayed in a particular date_sub calculation (and possibly other selects with date arithmetic, trying to figure out how to track them down is part of the goal of this post) where we aren't expecting them. MariaDB [testdb]> show variables like '%version%'; +-------------------------+---------------------+ | Variable_name | Value | +-------------------------+---------------------+ | innodb_version | 5.5.43-MariaDB-37.2 | | protocol_version | 10 | | slave_type_conversions | | | version | 5.5.44-MariaDB-log | | version_comment | MariaDB Server | | version_compile_machine | x86_64 | | version_compile_os | Linux | +-------------------------+---------------------+ 7 rows in set (0.00 sec) MariaDB [testdb]> show create table test \G *************************** 1. row *************************** Table: test Create Table: CREATE TABLE `test` ( `datetime` datetime NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 1 row in set (0.00 sec) MariaDB [testdb]> select datetime from test; Field 1: `datetime` Catalog: `def` Database: `velocitynorep` Table: `test` Org_table: `test` Type: DATETIME Collation: binary (63) Length: 19 Max_length: 19 Decimals: 0 Flags: NOT_NULL BINARY NO_DEFAULT_VALUE +---------------------+ | datetime | +---------------------+ | 2015-09-18 09:23:21 | +---------------------+ 1 row in set (0.00 sec) MariaDB [testdb]> select date_sub(datetime,interval 1 second) from test; Field 1: `date_sub(datetime,interval 1 second)` Catalog: `def` Database: `` Table: `` Org_table: `` Type: DATETIME Collation: binary (63) Length: 19 Max_length: 19 Decimals: 0 Flags: BINARY +--------------------------------------+ | date_sub(datetime,interval 1 second) | +--------------------------------------+ | 2015-09-18 09:23:20 | +--------------------------------------+ 1 row in set (0.00 sec) MariaDB [testdb]> select substr(datetime,1,13) from test; Field 1: `substr(datetime,1,13)` Catalog: `def` Database: `` Table: `` Org_table: `` Type: VAR_STRING Collation: utf8_general_ci (33) Length: 39 Max_length: 13 Decimals: 31 Flags: NOT_NULL +-----------------------+ | substr(datetime,1,13) | +-----------------------+ | 2015-09-18 09 | +-----------------------+ 1 row in set (0.00 sec) MariaDB [testdb]> select concat(substr(datetime,1,13),':00:00') -> from test; Field 1: `concat(substr(datetime,1,13),':00:00')` Catalog: `def` Database: `` Table: `` Org_table: `` Type: VAR_STRING Collation: utf8_general_ci (33) Length: 57 Max_length: 19 Decimals: 31 Flags: NOT_NULL +----------------------------------------+ | concat(substr(datetime,1,13),':00:00') | +----------------------------------------+ | 2015-09-18 09:00:00 | +----------------------------------------+ 1 row in set (0.00 sec) MariaDB [testdb]> select concat('2015-09-18 09',':00:00'); Field 1: `concat('2015-09-18 09',':00:00')` Catalog: `def` Database: `` Table: `` Org_table: `` Type: VAR_STRING Collation: utf8_general_ci (33) Length: 57 Max_length: 19 Decimals: 31 Flags: NOT_NULL +----------------------------------+ | concat('2015-09-18 09',':00:00') | +----------------------------------+ | 2015-09-18 09:00:00 | +----------------------------------+ 1 row in set (0.00 sec) MariaDB [testdb]> select date_sub(concat('2015-09-18 09',':00:00'), -> interval 1 second); Field 1: `date_sub(concat('2015-09-18 09',':00:00'), interval 1 second)` Catalog: `def` Database: `` Table: `` Org_table: `` Type: STRING Collation: binary (63) Length: 19 Max_length: 19 Decimals: 0 Flags: BINARY +---------------------------------------------------------------+ | date_sub(concat('2015-09-18 09',':00:00'), interval 1 second) | +---------------------------------------------------------------+ | 2015-09-18 08:59:59 | +---------------------------------------------------------------+ 1 row in set (0.00 sec) MariaDB [testdb]> select -> date_sub(concat(substr(datetime,1,13),':00:00'), -> interval 1 second) from test; Field 1: `date_sub(concat(substr(datetime,1,13),':00:00'), interval 1 second)` Catalog: `def` Database: `` Table: `` Org_table: `` Type: STRING Collation: binary (63) Length: 26 Max_length: 26 Decimals: 6 Flags: BINARY +---------------------------------------------------------------------+ | date_sub(concat(substr(datetime,1,13),':00:00'), interval 1 second) | +---------------------------------------------------------------------+ | 2015-09-18 08:59:59.000000 | +---------------------------------------------------------------------+ 1 row in set (0.00 sec) The last one is the one that has me stumped. 1.) Why does it include milliseconds in the output? According to this page: https://mariadb.com/kb/en/mariadb/microseconds-in-mariadb/ where no precision is specified the result should not display milliseconds, which is what happens in all the other examples above except this one. 2.) The statement on a 5.1 MySQL server (5.1.73-log, also 64 bit Linux) produces this: mysql> select date_sub(concat(substr(datetime,1,13),':00:00'), -> interval 1 second) from test; Field 1: `date_sub(concat(substr(datetime,1,13),':00:00'), interval 1 second)` Catalog: `def` Database: `` Table: `` Org_table: `` Type: STRING Collation: binary (63) Length: 29 Max_length: 19 Decimals: 31 Flags: BINARY +---------------------------------------------------------------------+ | date_sub(concat(substr(datetime,1,13),':00:00'), interval 1 second) | +---------------------------------------------------------------------+ | 2015-09-18 08:59:59 | +---------------------------------------------------------------------+ 1 row in set (0.00 sec) Is there some global variable I can set to revert to the 5.1 behavior? I realize I can CAST the result to a datetime to make sure I don't get the fractional seconds, but as I mentioned we're converting our system over to 5.5 and there's boatloads of code that I would have to scan through to try and find these differences. 3.) If there is no way to revert to the 5.1 behavior, can someone help me to understand the exact reason why the milliseconds get displayed on the final select in MariaDB 5.5? I'll need to look for any similar types of results and other than the exact reduction above I'm not sure what statements I would need to identify and test. Thanks for any assistance! Dan Ragle