====== Sort Key ======

**What it is:** An optional secondary key that, combined with partition key, forms a composite primary key.

**What it’s for:**
  * Query multiple related items within the same partition key (range queries).
  * Organize items by time or category (e.g., userId + timestamp).

**Key ideas:**
  * Allows efficient queries like “all orders for user X between time A and B”.

**Hard words:**
  * *composite* /kəmˈpɑːzɪt/: kết hợp
  * *range query* /reɪndʒ ˈkwɪri/: truy vấn theo khoảng