Use dates from Data A to indicate events in Data B

Hi, 

Apologise if this has been discussed as I am sure it has I just got find it  If so please leave a link to the discussion. 

Would like to use the dates in data A (excel sheet), to highlight the corresponding dates in data B (excel sheet) as to indicate significant events. For the use of a time series graphic. 

I have tried the operators Append, Join, and Union numerous times with no luck. 

Each data set when run succeeds and successfully produce individual tables. 

Thank you for any assistance on the matter.