#23678: Database default not removed if default=None
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Reporter: timgraham | Owner: nobody
Type: Bug | Status: closed
Component: Migrations | Version: 1.7
Severity: Release blocker | Resolution: worksforme
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by carljm):
* status: new => closed
* resolution: => worksforme
Comment:
Replying to [comment:2 loic]:
> @paulcdejean how do you get those results? I just tried with the
`sqlmigrate` command on initial migration on MySQL and my
`models.CharField(max_length=42, null=True)` doesn't show a DEFAULT.
You can see the difference as described if you actually run the migration
and then check `show create table tablename` in MySQL.
However, I am not convinced that this reflects a bug in Django, as opposed
to just a slightly odd behavior of `show create table` in MySQL. (I am not
very familiar with MySQL, so I could well be missing something).
For one thing, this difference doesn't show up in `describe tablename`:
all nullable fields with no other default show `NULL` in the "default"
column, regardless of whether they show `DEFAULT NULL` in the `show create
table tablename` output or not.
Secondly, if I add a column directly in MySQL (no involvement from Django)
using this exact syntax: `ALTER TABLE 'testapp_thing' ADD COLUMN 'direct'
varchar(100);` (note that I did not specify `DEFAULT NULL`, or any other
default), this is what `show create table testapp_thing` gives for that
column: `'direct' varchar(100) DEFAULT NULL,`. In other words, MySQL seems
to be adding that `DEFAULT NULL` itself, even if it wasn't in the `ALTER
TABLE`.
And lastly, I am not convinced that any of this matters anyway. The
nullable columns that do and don't show `DEFAULT NULL` in the `show create
table tablename` output seem to behave identically - they all in practice
still use `NULL` as their default value (consistent with the fact that
they all show `NULL` in the "default" column of their `describe` output).
My conclusion: `NULL` is the "default default" for any nullable column
without another explicit default value. There is no issue in Django here,
just some strange (but harmless) behavior from MySQL.
Closing; please reopen if you can provide further evidence that this is a
problem in Django.
--
Ticket URL: <https://code.djangoproject.com/ticket/23678#comment:3>
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