Setting TIME field to NULL with Zend_Db - mysql

Question

I came across what looks like an odd issue with either Zend_Db or PHP's PDO MySQL driver, that perhaps stems from my lack of knowledge of those two.
Let's assume I have a MySQL Table with a NULLable TIME field. If I run a query like this in MySQL client:
UPDATE mytable SET mytime = NULL WHERE id = 1;
Everything works as expected and mytime field will hold NULL as value after this query.
However, if I run the exact same query in PHP through the Zend_Db_Adapter, the mytime field is set to '0:0:0' after such query:
$db->getConnection()->exec('UPDATE mytable SET mytime = NULL WHERE id = 1');
How do I set that TIME field to NULL?
I'm using PHP5.3 with PDO MySQL driver, Zend Framework 1.11 and MySQL 5.1.

Answer 1

What you have should work, i.e.:
$db->getConnection()->exec('UPDATE mytable SET mytime = NULL WHERE id = 1');
That should work. I tested it.
Caveat
If the data type time is NOT NULL, then trying to set it to NULL will cause the value NULL to be defaulted to 00:00:00, which may be unexpected behaviour e.g.:
CREATE TABLE `test` (
`time` datetime NOT NULL
);
Trying to insert or update the time field above with NULL will cause the value 00:00:00 to be inserted.
This is similar for date, datetime, and a few other data types. e.g. Trying to set a data type datetime which is NOT NULL to NULL will default its value to 0000-00-00 00:00:00.
NOTE: Mysql will not throw an error when you try to set a NULL value to a NUT NULL data type, you can change this behaviour by setting MySQL's SQL_MODE to STRICT_ALL_TABLES: see this stackoverflow question.
The Fix
Change the field to allow NULL and it should be fine:
CREATE TABLE `test` (
`time` datetime DEFAULT NULL
);
Now the time field can be set to NULL.

Answer 2

use new Zend_Db_Expr('NULL') instead of NULL :
$zend_null = new Zend_Db_Expr('NULL');
$db->getConnection()->exec("UPDATE mytable SET mytime = $zend_null WHERE id = 1");