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Upgrading to MySQL 5.7? Beware of the new STRICT mode

October 18, 2016

Author

Alexander Rubin

MySQL

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This blog post discusses the ramifications of STRICT mode in MySQL 5.7.

In short

By default, MySQL 5.7 is much “stricter” than older versions of MySQL. That can make your application fail. To temporarily fix this, change the SQL_MODE to NO_ENGINE_SUBSTITUTION (same as in MySQL 5.6):

mysql> set global SQL_MODE="NO_ENGINE_SUBSTITUTION";

1	mysql> set global SQL_MODE="NO_ENGINE_SUBSTITUTION";

MySQL 5.7, dates and default values

The default SQL_MODE in MySQL 5.7 is:

ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

1	ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

That makes MySQL operate in “strict” mode for transactional tables.

“Strict mode controls how MySQL handles invalid or missing values in data-change statements such as INSERT or UPDATE. A value can be invalid for several reasons. For example, it might have the wrong data type for the column, or it might be out of range. A value is missing when a new row to be inserted does not contain a value for a non-NULL column that has no explicit DEFAULT clause in its definition. (For a NULL column, NULL is inserted if the value is missing.) Strict mode also affects DDL statements such as CREATE TABLE.”

http://dev.mysql.com/doc/refman/5.7/en/sql-mode.html#sql-mode-strict

That also brings up an interesting problem with the default value for the date/datetime column. Let’s say we have the following table in MySQL 5.7, and want to insert a row into it:

mysql> CREATE TABLE `events_t` (
-> `id` int(11) NOT NULL AUTO_INCREMENT,
-> `event_date` datetime NOT NULL,
-> `profile_id` int(11) DEFAULT NULL,
-> PRIMARY KEY (`id`),
-> KEY `event_date` (`event_date`),
-> KEY `profile_id` (`profile_id`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=latin1
-> ;
Query OK, 0 rows affected (0.02 sec)

mysql> insert into events_t (profile_id) values (1);
ERROR 1364 (HY000): Field 'event_date' doesn't have a default value

mysql> CREATE TABLE `events_t` (

-> `id` int(11) NOT NULL AUTO_INCREMENT,

-> `event_date` datetime NOT NULL,

-> `profile_id` int(11) DEFAULT NULL,

-> PRIMARY KEY (`id`),

-> KEY `event_date` (`event_date`),

-> KEY `profile_id` (`profile_id`)

-> ) ENGINE=InnoDB DEFAULT CHARSET=latin1

-> ;

Query OK, 0 rows affected (0.02 sec)

mysql> insert into events_t (profile_id) values (1);

ERROR 1364 (HY000): Field 'event_date' doesn't have a default value

The event_date does not have a default value, and we are inserting a row without a value for event_date. That causes an error in MySQL 5.7. If we can’t use NULL, we will have to create a default value. In strict mod,e we can’t use “0000-00-00” either:

mysql> alter table events_t change event_date event_date datetime NOT NULL default '0000-00-00 00:00:00';
ERROR 1067 (42000): Invalid default value for 'event_date'
mysql> alter table events_t change event_date event_date datetime NOT NULL default '2000-00-00 00:00:00';
ERROR 1067 (42000): Invalid default value for 'event_date'

mysql> alter table events_t change event_date event_date datetime NOT NULL default '0000-00-00 00:00:00';

ERROR 1067 (42000): Invalid default value for 'event_date'

mysql> alter table events_t change event_date event_date datetime NOT NULL default '2000-00-00 00:00:00';

ERROR 1067 (42000): Invalid default value for 'event_date'

We have to use a real date:

mysql> alter table events_t change event_date event_date datetime NOT NULL default '2000-01-01 00:00:00';
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> insert into events_t (profile_id) values (1);
Query OK, 1 row affected (0.00 sec)

mysql> alter table events_t change event_date event_date datetime NOT NULL default '2000-01-01 00:00:00';

Query OK, 0 rows affected (0.00 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> insert into events_t (profile_id) values (1);

Query OK, 1 row affected (0.00 sec)

Or, a most likely much better approach is to change the application logic to:

- allow NULLs, or

- always insert the real dates (i.e. use NOW() function), or

- change the table field to timestamp and update it automatically if no value has been assigned

I see and microseconds are important to us, regular humans. I fail to see how but then that’s just me, a normal human being. The boys at MySQL are obviously not from this galaxy and are superbeings. I’m trying to change the field to VARCHAR but guess what PHPMyAdmin (another bright light in the chandeleer) gives error on the other date field. So if you have 2 date fields you cannot even change one of them. Great guys. Keep up the good work!