====== Local Secondary Index (LSI) ======

**What it is:** A secondary index that uses the same partition key as the base table but a different sort key.

**What it’s for:**
  * Query different sort orders within the same partition key.

**Key ideas:**
  * Must be created at table creation time (typical exam point).
  * Useful when you know the access pattern early.

**Exam cues:**
  * “need same partition key but alternate sort key” → LSI.

**Hard words:**
  * *local* /ˈloʊkəl/: cục bộ (cùng partition key)
  * *created at table creation* /kriˈeɪtɪd æt ˈteɪbl kriˈeɪʃn/: phải tạo lúc tạo bảng