Fixed #26500 -- Added SKIP LOCKED support to select_for_update().

Thanks Tim for the review.

2 files changed, 9 insertions, 4 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index cedb140143..5eaac1fc74 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -445,13 +445,16 @@ class SQLCompiler(object):
                         "select_for_update cannot be used outside of a transaction."
                     )
 
-                # If we've been asked for a NOWAIT query but the backend does
-                # not support it, raise a DatabaseError otherwise we could get
-                # an unexpected deadlock.
                 nowait = self.query.select_for_update_nowait
+                skip_locked = self.query.select_for_update_skip_locked
+                # If we've been asked for a NOWAIT/SKIP LOCKED query but the
+                # backend does not support it, raise a DatabaseError otherwise
+                # we could get an unexpected deadlock.
                 if nowait and not self.connection.features.has_select_for_update_nowait:
                     raise DatabaseError('NOWAIT is not supported on this database backend.')
-                result.append(self.connection.ops.for_update_sql(nowait=nowait))
+                elif skip_locked and not self.connection.features.has_select_for_update_skip_locked:
+                    raise DatabaseError('SKIP LOCKED is not supported on this database backend.')
+                result.append(self.connection.ops.for_update_sql(nowait=nowait, skip_locked=skip_locked))
 
             return ' '.join(result), tuple(params)
         finally:
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index d182242ce4..426087f8af 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -167,6 +167,7 @@ class Query(object):
         self.distinct_fields = []
         self.select_for_update = False
         self.select_for_update_nowait = False
+        self.select_for_update_skip_locked = False
 
         self.select_related = False
         # Arbitrary limit for select_related to prevents infinite recursion.
@@ -286,6 +287,7 @@ class Query(object):
         obj.distinct_fields = self.distinct_fields[:]
         obj.select_for_update = self.select_for_update
         obj.select_for_update_nowait = self.select_for_update_nowait
+        obj.select_for_update_skip_locked = self.select_for_update_skip_locked
         obj.select_related = self.select_related
         obj.values_select = self.values_select[:]
         obj._annotations = self._annotations.copy() if self._annotations is not None else None