Primary keys that are most likely natural keys

Author: mfvanek

README.md

@@ -53,6 +53,7 @@ For more information please see [PostgreSQL Versioning Policy](https://www.postg
 29. Primary keys with varchar columns instead of uuids ([sql](https://github.com/mfvanek/pg-index-health-sql/blob/master/sql/primary_keys_with_varchar.sql)).
 30. Columns with [varchar(n)](https://www.postgresql.org/docs/current/datatype-character.html) type ([sql](https://github.com/mfvanek/pg-index-health-sql/blob/master/sql/columns_with_fixed_length_varchar.sql)).
 31. Indexes with unnecessary where-clause on not null column ([sql](https://github.com/mfvanek/pg-index-health-sql/blob/master/sql/indexes_with_unnecessary_where_clause.sql)).
+32. Primary keys that are most likely natural keys ([sql](https://github.com/mfvanek/pg-index-health-sql/blob/master/sql/primary_keys_that_most_likely_natural_keys.sql)).
 
 ## Local development
 

sql/primary_keys_that_most_likely_natural_keys.sql

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2019-2025. Ivan Vakhrushev and others.
+ * https://github.com/mfvanek/pg-index-health-sql
+ *
+ * Licensed under the Apache License 2.0
+ */
+
+-- Finds primary keys that are most likely natural keys.
+-- It is better to use surrogate keys instead of natural ones.
+-- See https://www.youtube.com/watch?v=s6m8Aby2at8
+-- See also https://www.databasestar.com/database-keys/
+with
+    nsp as (
+        select
+            nsp.oid,
+            nsp.nspname
+        from pg_catalog.pg_namespace nsp
+        where
+            nsp.nspname = :schema_name_param::text
+    )
+
+select
+    t.oid::regclass::text as table_name,
+    c.conindid::regclass::text as index_name,
+    pg_relation_size(c.conindid) as index_size,
+    array_agg(quote_ident(col.attname) || ',' || col.attnotnull::text order by u.attposition) as columns
+from
+    pg_catalog.pg_constraint c
+    inner join pg_catalog.pg_class t on t.oid = c.conrelid
+    inner join nsp on nsp.oid = c.connamespace
+    inner join lateral unnest(c.conkey) with ordinality u(attnum, attposition) on true
+    inner join pg_catalog.pg_attribute col on col.attrelid = t.oid and col.attnum = u.attnum
+where
+    c.contype = 'p' and /* primary key constraint */
+    c.conparentid = 0 and c.coninhcount = 0 and /* not a constraint in a partition */
+    t.relkind = 'r' /* only regular tables */
+group by t.oid, c.conindid
+having bool_or(
+    col.atttypid not in (
+        'smallint'::regtype,
+        'integer'::regtype,
+        'bigint'::regtype,
+        'uuid'::regtype
+    )
+)
+
+union all
+
+select
+    t.oid::regclass::text as table_name,
+    c.conindid::regclass::text as index_name,
+    pg_relation_size(c.conindid) as index_size,
+    array_agg(quote_ident(col.attname) || ',' || col.attnotnull::text order by u.attposition) as columns
+from
+    pg_catalog.pg_constraint c
+    inner join pg_catalog.pg_class t on t.oid = c.conrelid
+    inner join nsp on nsp.oid = c.connamespace
+    inner join lateral unnest(c.conkey) with ordinality u(attnum, attposition) on true
+    inner join pg_catalog.pg_attribute col on col.attrelid = t.oid and col.attnum = u.attnum
+where
+    c.contype = 'p' and /* primary key constraint */
+    c.conparentid = 0 and c.coninhcount = 0 and /* not a constraint in a partition */
+    t.relkind = 'p' and /* only partitioned tables */
+    not t.relispartition
+group by t.oid, c.conindid
+having bool_or(
+    /* for partitioned tables decided to allow a few more data types that usually are used in ranges */
+    col.atttypid not in (
+        'smallint'::regtype,
+        'integer'::regtype,
+        'bigint'::regtype,
+        'uuid'::regtype,
+        'date'::regtype,
+        'timestamp'::regtype,
+        'timestamptz'::regtype,
+        'time'::regtype,
+        'timetz'::regtype
+    )
+)
+order by table_name, index_name;