fix: Fix cascade delete for multi-column FKs and renamed attributes

Two critical fixes for PostgreSQL cascade delete:

1. Fix PostgreSQL constraint info query to properly match FK columns
   - Use referential_constraints to join FK and PK columns by position
   - Previous query returned cross product of all columns
   - Now returns correct matched pairs: (fk_col, parent_table, pk_col)

2. Fix Heading.select() to preserve table_info (adapter context)
   - Projections with renamed attributes need adapter for quoting
   - New heading now inherits table_info from parent heading
   - Prevents fallback to backticks on PostgreSQL

All cascade delete tests now passing:
- test_simple_cascade_delete[postgresql] ✅
- test_multi_level_cascade_delete[postgresql] ✅
- test_cascade_delete_with_renamed_attrs[postgresql] ✅

All unit tests passing (212/212).
All multi-backend tests passing (4/4).

Author: dimitri-yatsenko

src/datajoint/adapters/postgres.py

@@ -668,16 +668,25 @@ def get_foreign_keys_sql(self, schema_name: str, table_name: str) -> str:
         )
 
     def get_constraint_info_sql(self, constraint_name: str, schema_name: str, table_name: str) -> str:
-        """Query to get FK constraint details from information_schema."""
+        """
+        Query to get FK constraint details from information_schema.
+
+        Returns matched pairs of (fk_column, parent_table, pk_column) for each
+        column in the foreign key constraint, ordered by position.
+        """
         return (
             "SELECT "
             "  kcu.column_name as fk_attrs, "
             "  '\"' || ccu.table_schema || '\".\"' || ccu.table_name || '\"' as parent, "
             "  ccu.column_name as pk_attrs "
             "FROM information_schema.key_column_usage AS kcu "
-            "JOIN information_schema.constraint_column_usage AS ccu "
-            "  ON kcu.constraint_name = ccu.constraint_name "
-            "  AND kcu.constraint_schema = ccu.constraint_schema "
+            "JOIN information_schema.referential_constraints AS rc "
+            "  ON kcu.constraint_name = rc.constraint_name "
+            "  AND kcu.constraint_schema = rc.constraint_schema "
+            "JOIN information_schema.key_column_usage AS ccu "
+            "  ON rc.unique_constraint_name = ccu.constraint_name "
+            "  AND rc.unique_constraint_schema = ccu.constraint_schema "
+            "  AND kcu.ordinal_position = ccu.ordinal_position "
             "WHERE kcu.constraint_name = %s "
             "  AND kcu.table_schema = %s "
             "  AND kcu.table_name = %s "

src/datajoint/heading.py

@@ -604,7 +604,10 @@ def select(self, select_list, rename_map=None, compute_map=None):
             dict(default_attribute_properties, name=new_name, attribute_expression=expr)
             for new_name, expr in compute_map.items()
         )
-        return Heading(chain(copy_attrs, compute_attrs), lineage_available=self._lineage_available)
+        # Inherit table_info so the new heading has access to the adapter
+        new_heading = Heading(chain(copy_attrs, compute_attrs), lineage_available=self._lineage_available)
+        new_heading.table_info = self.table_info
+        return new_heading
 
     def _join_dependent(self, dependent):
         """Build attribute list when self → dependent: PK = PK(self), self's attrs first."""