云函数访问数据库调用cond函数出错，提示没有operator?
Error: errCode: -502001 database request fail | errMsg: [FailedOperation] (BadValue) unknown top level operator: $cond;
at Object.returnAsCloudSDKError
at Object.checkError
at cloudfunctions/getExp/node_modules/wx-server-sdk/index.js:1150:33
at processTicksAndRejections
