Fixed #23576 -- Implemented multi-alias fast-path deletion in MySQL backend.

This required moving the entirety of DELETE SQL generation to the
compiler where it should have been in the first place and implementing
a specialized compiler on MySQL/MariaDB.

The MySQL compiler relies on the "DELETE table FROM table JOIN" syntax
for queries spanning over multiple tables.

1 files changed, 0 insertions, 35 deletions

diff --git a/django/db/models/sql/subqueries.py b/django/db/models/sql/subqueries.py
index fbc265d113..af48239cdc 100644
--- a/django/db/models/sql/subqueries.py
+++ b/django/db/models/sql/subqueries.py
@@ -3,7 +3,6 @@ Query subclasses which provide extra functionality beyond simple data retrieval.
 """
 
 from django.core.exceptions import FieldError
-from django.db import connections
 from django.db.models.query_utils import Q
 from django.db.models.sql.constants import (
     CURSOR, GET_ITERATOR_CHUNK_SIZE, NO_RESULTS,
@@ -41,40 +40,6 @@ class DeleteQuery(Query):
             num_deleted += self.do_query(self.get_meta().db_table, self.where, using=using)
         return num_deleted
 
-    def delete_qs(self, query, using):
-        """
-        Delete the queryset in one SQL query (if possible). For simple queries
-        this is done by copying the query.query.where to self.query, for
-        complex queries by using subquery.
-        """
-        innerq = query.query
-        # Make sure the inner query has at least one table in use.
-        innerq.get_initial_alias()
-        # The same for our new query.
-        self.get_initial_alias()
-        innerq_used_tables = tuple([t for t in innerq.alias_map if innerq.alias_refcount[t]])
-        if not innerq_used_tables or innerq_used_tables == tuple(self.alias_map):
-            # There is only the base table in use in the query.
-            self.where = innerq.where
-        else:
-            pk = query.model._meta.pk
-            if not connections[using].features.update_can_self_select:
-                # We can't do the delete using subquery.
-                values = list(query.values_list('pk', flat=True))
-                if not values:
-                    return 0
-                return self.delete_batch(values, using)
-            else:
-                innerq.clear_select_clause()
-                innerq.select = [
-                    pk.get_col(self.get_initial_alias())
-                ]
-                values = innerq
-            self.where = self.where_class()
-            self.add_q(Q(pk__in=values))
-        cursor = self.get_compiler(using).execute_sql(CURSOR)
-        return cursor.rowcount if cursor else 0
-
 
 class UpdateQuery(Query):
     """An UPDATE SQL query."""