[3.2.x] Fixed #32793 -- Fixed loss of precision for temporal operations with DecimalFields on MySQL.

Regression in 1e38f1191de21b6e96736f58df57dfb851a28c1f.

Thanks Mohsen Tamiz for the report.
Backport of e703b152c6148ddda1b072a4353e9a41dca87f90 from main

2 files changed, 9 insertions, 1 deletions

diff --git a/tests/expressions/models.py b/tests/expressions/models.py
index 02836e653e..bd6be81c5f 100644
--- a/tests/expressions/models.py
+++ b/tests/expressions/models.py
@@ -48,9 +48,10 @@ class Company(models.Model):
 class Number(models.Model):
     integer = models.BigIntegerField(db_column='the_integer')
     float = models.FloatField(null=True, db_column='the_float')
+    decimal_value = models.DecimalField(max_digits=20, decimal_places=17, null=True)
 
     def __str__(self):
-        return '%i, %.3f' % (self.integer, self.float)
+        return '%i, %.3f, %.17f' % (self.integer, self.float, self.decimal_value)
 
 
 class Experiment(models.Model):
diff --git a/tests/expressions/tests.py b/tests/expressions/tests.py
index bea7633a49..728c4051c5 100644
--- a/tests/expressions/tests.py
+++ b/tests/expressions/tests.py
@@ -1176,6 +1176,13 @@ class ExpressionsNumericTests(TestCase):
         self.assertEqual(Number.objects.get(pk=n.pk).integer, 10)
         self.assertEqual(Number.objects.get(pk=n.pk).float, Approximate(256.900, places=3))
 
+    def test_decimal_expression(self):
+        n = Number.objects.create(integer=1, decimal_value=Decimal('0.5'))
+        n.decimal_value = F('decimal_value') - Decimal('0.4')
+        n.save()
+        n.refresh_from_db()
+        self.assertEqual(n.decimal_value, Decimal('0.1'))
+
 
 class ExpressionOperatorTests(TestCase):
     @classmethod