diff --git a/docs/uniCloud/cf-database.md b/docs/uniCloud/cf-database.md
index 380f260236c6791c33a29076d8dc723dc346e22f..b1bade14ca5d974667ca724815224f53172e283d 100644
--- a/docs/uniCloud/cf-database.md
+++ b/docs/uniCloud/cf-database.md
@@ -434,7 +434,7 @@ let res = await db.collection('goods').where({
 ```js
 const dbCmd = db.command
 let res = await db.collection('goods').where({
-  _db: dbCmd.exists(true)
+  _id: dbCmd.exists(true)
 }).count()
 ```