Clustered Index (id) " C # B " D $ B # D # G " E $ F SecondaryIndex (user_id, friend_id) SecondaryIndex (friend_id) icon: https://www.iconfinder.com/icons/174603/deciduous_tree_icon#size=256
# D # G $ B $ F SecondaryIndex (user_id, friend_id) Clustered Index (id) SecondaryIndex (friend_id) icon: https://www.iconfinder.com/icons/174603/deciduous_tree_icon#size=256