you can achieve this by iteration process over the keys by using stub.GetStateByRange() function.
I have included an example below. Go through it and try to implement on of ur own.
keysIter, err := stub.GetStateByRange(startKey, endKey)
if err != nil {
return shim.Error(fmt.Sprintf("keys operation failed. Error accessing state: %s", err))
}
defer keysIter.Close()
var keys []string
for keysIter.HasNext() {
key, _, iterErr := keysIter.Next()
if iterErr != nil {
return shim.Error(fmt.Sprintf("keys operation failed. Error accessing state: %s", err))
}
keys = append(keys, key)
}