SQL problem in HANA Studio CalculationView

Dear all,

I'm working on a simple SQL-statement in HANA studio for merging two tables. I'm using a SQL-script Calculation View and want to combine these tables. The structure of the two tables is the following:

Table A: ChangeDocument

Table B: ChangeLog

I wrote the following SQL-Statement:

var_out =  SELECT A.ChangeDate AS"ChangeDate", A.DocumentNo AS"DocumentNo", B.DocumentNo,

           B.ObjectValue AS"ObjectValue", B.OldValue AS"OldValue", B.NewValue AS"NewValue"

           FROM ChangeDocument AS A LEFT JOIN ChangeLog AS B

           ON A.DocumentNo=B.DocumentNo

           GROUP BY DocumentNo;

Unfortunately, I receive the following error, when I'm trying the excute the statement:

Deploy Calculation View: SQL: transaction rolled back by an internal error: invalid column name: A.DOCUMENTNO

I really appreciate your help.

Regards

Dirk