JQコマンドでJSONの特定の値を抽出したい

JQコマンドでのJSONの加工をして、特定の値のみ抽出したいのですが、
マニュアルやサイトを見て、いろいろ試行錯誤したのですが、
どうしたらよいかわかりません。
どなたか、助けていただけないでしょうか？

詳細は、下記のようになります。

元データ

[
  {
    "room_id": 99999999,
    "name": "佐藤一郎",
    "type": "direct",
    "role": "member",
    "sticky": true,
    "unread_num": 2,
    "mention_num": 1,
    "mytask_num": 0,
    "message_num": 28,
    "file_num": 3,
    "task_num": 0,
    "icon_path": "https://appdata.chatwork.com/avatar/99999999/99999999.png",
    "last_update_time": 1556586317
  },
 {
    "room_id": 88888888,
    "name": "山田 花子",
    "type": "direct",
    "role": "member",
    "sticky": false,
    "unread_num": 0,
    "mention_num": 0,
    "mytask_num": 0,
    "message_num": 1,
    "file_num": 0,
    "task_num": 0,
    "icon_path": "https://appdata.chatwork.com/avatar/88888888/88888888.rsz.jpg",
    "last_update_time": 88888888
  }
]

得たい結果

999999999
88888888

試したコマンドと実行結果

$ curl -X GET -H "X-ChatWorkToken: XXXXXXXX" "https://api.chatwork.com/v2/rooms/" | jq 'room_id'

jq: error: room_id/0 is not defined at <top-level>, line 1:
room_id
jq: 1 compile error
curl: (23) Failed writing body (0 != 16384)

$ curl -X GET -H "X-ChatWorkToken: XXXXXXXX" "https://api.chatwork.com/v2/rooms/" | jq '.room_id'

jq: error (at <stdin>:0): Cannot index array with string "room_id"

$ curl -X GET -H "X-ChatWorkToken: XXXXXXXX" "https://api.chatwork.com/v2/rooms/" | jq '[room_id]'

jq: error: room_id/0 is not defined at <top-level>, line 1:
[room_id] 
jq: 1 compile error
curl: (23) Failed writing body (0 != 16384)

$ curl -X GET -H "X-ChatWorkToken: XXXXXXXX" "https://api.chatwork.com/v2/rooms/" | jq '[.room_id]'

jq: error (at <stdin>:0): Cannot index array with string "room_id"

$ curl -X GET -H "X-ChatWorkToken: XXXXXXXX" "https://api.chatwork.com/v2/rooms/" | jq '[{room_id}]'

jq: error (at <stdin>:0): Cannot index array with string "room_id"

$ curl -X GET -H "X-ChatWorkToken: XXXXXXXX" "https://api.chatwork.com/v2/rooms/" | jq '[{.room_id}]'

jq: error: syntax error, unexpected FIELD (Unix shell quoting issues?) at <top-level>, line 1:
[{.room_id}]  
jq: 1 compile error
curl: (23) Failed writing body (0 != 16384)