[MongoDB] index

Level 0 (Root)
+-----------------------------+
|         [30 | 60]           |   루트 노드 (최상위)
+-----------------------------+
        /           |           \
       /            |            \
Level 1       Level 1        Level 1
+-----------+ +-----------+ +-----------+
| [10|20]   | | [40|50]   | | [70|80|90]|
+-----------+ +-----------+ +-----------+
   /   \         /   \          /   |   \
  /     \       /     \        /    |    \
L2      L2     L2     L2    L2    L2    L2



------

db.users.createIndex({email : 1})


db.users.createindex({userId : 1, status : 1, createdAt : 1})
-> 정합한 예 : db.users.find({userid : 100, status : "paid"}).sort({createdAt : -1})
-> 조금 아쉬운 쿼리 : db.users.find({userid : 100, status : "paid"})
-> 잘못된 쿼리 : db.users.find({status : "paid"})