Use pg_index's indnatts when indnkeyatts is not available

Using NULL when this column is not available does not work with old
PostgreSQL (tested on version 9.6, as reported in #12600).

Instead, use `indnatts` which should be equal to what `indnkeyatts` would be
as there is no "included attributes" in the index on these old versions
(but only "key columns").

From https://www.postgresql.org/docs/17/catalog-pg-index.html:
* `indnatts`, "The total number of columns in the index [...]; this number
  includes both key and included attributes"
* `indnkeyatts`, "The number of key columns in the index, not counting any
  included columns [...]"

Fixes #12600.

diff --git a/doc/build/changelog/unreleased_20/12600.rst b/doc/build/changelog/unreleased_20/12600.rst
new file mode 100644 (file)
index 0000000..99d8b6b
--- /dev/null
+++ b/doc/build/changelog/unreleased_20/12600.rst
@@ -0,0 +1,6 @@
+.. change::
+    :tags: bug, postgresql
+    :tickets: 12600
+
+    Fix query for unique and primary key constraints reflection on PostgreSQL 10
+    and below.

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index ee4a168e377d48f0cb5524ffde487b7d5a1355db..3d0fff2890d564adff763d59066b43d2c3b998ed 100644 (file)
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -4110,7 +4110,7 @@ class PGDialect(default.DefaultDialect):
         if self.server_version_info >= (11, 0):
             indnkeyatts = pg_catalog.pg_index.c.indnkeyatts
         else:
-            indnkeyatts = sql.null().label("indnkeyatts")
+            indnkeyatts = pg_catalog.pg_index.c.indnatts.label("indnkeyatts")
 
         if self.server_version_info >= (15,):
             indnullsnotdistinct = pg_catalog.pg_index.c.indnullsnotdistinct
@@ -4585,7 +4585,7 @@ class PGDialect(default.DefaultDialect):
         if self.server_version_info >= (11, 0):
             indnkeyatts = pg_catalog.pg_index.c.indnkeyatts
         else:
-            indnkeyatts = sql.null().label("indnkeyatts")
+            indnkeyatts = pg_catalog.pg_index.c.indnatts.label("indnkeyatts")
 
         if self.server_version_info >= (15,):
             nulls_not_distinct = pg_catalog.pg_index.c.indnullsnotdistinct