DECLARE not working in SQL Console

Hi All:

I have many years of db development experience but am new to SAP HANA. It is puzzling that I cannot simply write a simple "DECLARE RowCount INT = 0;" in the SQL Console and execute it without getting error message. Why cannot that statement be executed in the SQL Console?

Also, there is a notion of a DUMMY table. I tried to find information about it but could not find anything. I know you cannot do SELECT 'Hello'; but this works SELECT 'Hello' FROM DUMMY;. What is the concept behind DUMMY?

Thank you;