id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
33802	Q objects to match an empty string in CheckConstraint results in invalid SQL using MySQL	Phil Gyford	nobody	"Using a constraint like that below results in a migration that generates invalid SQL when using a MariaDB (v10.3) database. I think it's OK using SQLite, but I haven't tried Postgresql.

{{{
from django.db import models
from django.db.models import Q

class Person(models.Model):
    firstname = models.CharField(max_length=50, blank=True, null=False, default="""")

    class Meta:
        constraints = [
            models.CheckConstraint(
                name=""%(app_label)s_%(class)s_firstname"",
                check=(Q(firstname__exact="""")),
            )
        ]
}}}

Running `manage.py makemigrations` results in a migration with this operation:

{{{
constraint=models.CheckConstraint(
    check=models.Q((""firstname__exact"", """")),
    name=""myapp_person_firstname"",
),
}}}

And running `manage.py sqlmigrate myapp 0002` shows this (note there should be a pair of empty quotes between `=` and `)` at the end):

{{{
ALTER TABLE `Person` ADD CONSTRAINT `myapp_person_firstname` CHECK (`firstname` = );
}}}

Unsurprisingly, running the migration results in:

{{{
django.db.utils.ProgrammingError: (1064, ""1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ')' at line 1"", '42000')
}}}
"	Bug	closed	Migrations	4.0	Normal	worksforme			Unreviewed	0	0	0	0	0	0