docs: update README and add PostgreSQL to stores documentation

- Remove PostgreSQL from README backends list to match main's simplified format
- Add docs/stores.md with PostgreSQL entry in distributed stores section
- Apply ruff formatting to PostgreSQL store

Co-authored-by: William Easton <strawgate@users.noreply.github.com>

Author: github-actions[bot]

README.md

@@ -17,8 +17,8 @@ This monorepo contains two libraries:
 
 ## Why use this library?
 
-- **Multiple backends**: DynamoDB, Elasticsearch, Memcached, MongoDB, PostgreSQL,
-  Redis, RocksDB, Valkey, and In-memory, Disk, etc
+- **Multiple backends**: DynamoDB, Elasticsearch, Memcached, MongoDB, Redis,
+  RocksDB, Valkey, and In-memory, Disk, etc
 - **TTL support**: Automatic expiration handling across all store types
 - **Type-safe**: Full type hints with Protocol-based interfaces
 - **Adapters**: Pydantic model support, raise-on-missing behavior, etc

docs/stores.md

@@ -331,6 +331,7 @@ Distributed stores provide network-based storage for multi-node applications.
 | Elasticsearch | Unstable | ✅ | ✅ | Full-text search with key-value capabilities |
 | Memcached | Unstable | ✅ | ✖️ | High-performance distributed memory cache |
 | MongoDB | Unstable | ✅ | ✅ | Document database used as key-value store |
+| PostgreSQL | Unstable | ✅ | ✖️ | PostgreSQL-based key-value storage |
 | Redis | Stable | ✅ | ✅ | Popular in-memory data structure store |
 | Valkey | Stable | ✅ | ✅ | Open-source Redis fork |
 
@@ -500,6 +501,49 @@ pip install py-key-value-aio[mongodb]
 
 ---
 
+### PostgreSQLStore
+
+PostgreSQL relational database used as a key-value store.
+
+```python
+from key_value.aio.stores.postgresql import PostgreSQLStore
+
+# Using connection URL
+store = PostgreSQLStore(url="postgresql://localhost:5432/mydb")
+
+# Using connection parameters
+store = PostgreSQLStore(
+    host="localhost",
+    port=5432,
+    database="mydb",
+    user="myuser",
+    password="mypass"
+)
+```
+
+**Installation:**
+
+```bash
+pip install py-key-value-aio[postgresql]
+```
+
+**Use Cases:**
+
+- Applications already using PostgreSQL
+- Need for SQL query capabilities
+- ACID compliance requirements
+- Relational data with key-value access pattern
+
+**Characteristics:**
+
+- JSONB storage for values
+- TTL support via expires_at timestamps
+- Optimized bulk operations
+- Lazy cleanup of expired entries
+- Stable storage format: **Unstable**
+
+---
+
 ### MemcachedStore
 
 High-performance distributed memory caching system.

key-value/key-value-aio/src/key_value/aio/stores/postgresql/store.py

@@ -270,6 +270,7 @@ async def _setup_collection(self, *, collection: str) -> None:
         index_name = f"idx_{self._table_name}_expires_at"
         if len(index_name) > POSTGRES_MAX_IDENTIFIER_LEN:
             import hashlib
+
             index_name = "idx_" + hashlib.sha256(self._table_name.encode()).hexdigest()[:16] + "_exp"
         create_index_sql = f"""  # noqa: S608
         CREATE INDEX IF NOT EXISTS {index_name}
@@ -439,8 +440,7 @@ async def _put_managed_entries(
 
         # Prepare data for batch insert using method-level ttl/created_at/expires_at
         values = [
-            (sanitized_collection, key, entry.value, ttl, created_at, expires_at)
-            for key, entry in zip(keys, managed_entries, strict=True)
+            (sanitized_collection, key, entry.value, ttl, created_at, expires_at) for key, entry in zip(keys, managed_entries, strict=True)
         ]
 
         async with self._acquire_connection() as conn: