how to merge table1 & table 2 in cloud database in appian?

Do you mean a database view? The database used is a MariaDB. As this is not specific to Appian, I recommend the MariaDB documentation.

If your use case allows, I recommend using Appian record relationships instead of views. 

If in your case one-to-many relationship can't have more than 10 fields then you can go for Record relationship otherwise you can use views for the same.