@Hubert Dudek​  @Kavya Manohar Parag​ 

Thanks for the input. I have tried running below command, it was succeeded.

"!nc -zv md1n4trqmokgnhr.csnrqwqko4ho.ap-southeast-1.rds.amazonaws.com 3306".

However, Database is not accessible. Please see the error comes for show databases.

Also, I have tried several trial accounts using this AWS account. Is there any restriction for trial accounts ?