Choose fields from different tables

[Anonymous]

Hi all, I was stuck at this problem for a long time.

I want to display the function below:

These data come from two main source:

1 I have a Table A. Table A records the historical records, including all fields above.

2 Another table B is recording the current data, which including "Client", "Program", "Occurrence","Event"  fields, and "No of Respondent", "Engagement","Learning","Commitment to apply", "Confidence to apply" are needed to be calculated by choosing some fields of table B.

Now the function I want to achieve is, depending on the selection of "Client","Programme","Occurrence", display different value come form table A or table B. So Can I use if statement to achieve this function? If yes, how can I use this? Should I use if expression in each column?  Any suggestions will be really appreciated...