As seen below, data is in the worksheet, the data on the left is the 2nd source of data. In the worksheet "Code" in column is the same as "Chief Complaint" on the 2nd data source however they are not related to one another. Currently there are 37 data points in the graph, once I add the 2nd data source, it should go up to 44.
I realize you're working with public-safety data and might not be able to upload it because of HIPPA and other data-sensitive issues, but is it possible to share the two data sources to the forums so we have a clearer understanding of what you're trying to join to?
If not, then based on the above screen shot, the only linking field that Tableau is currently recognizing as the same between your two sets of data is your Date Admitted field (gray chain link). What you're trying to do is blend two sets of data that have differently named field columns, but are essentially the same data types/elements.
If you go to the top menu in Tableau and click on Data, then click on Edit Relationships, a new dialog box will open up; then, click on the radio button Custom, then click on Add and you should see the field column values between the two data sources. Make sure that Code is highlighted on one side and Chief Complaint is highlighted on the other side and that should cause a recognized blend of the two sets of data based on that linkage. Examples are provide below:
As background, I formerly worked as the Exec. Admin. for a large 9-1-1 center here in LA County (now retired) and we were able to implement Tableau very successfully for our 14 fire departments, so I understand what you're trying to achieve here. Let me know if I can help any further or if this answered your issue, please mark it as correct so that others will be able to find it.
As Don said, you need to establish a relationship between your two tables.
If they don't have a relationship, you either need to reshape your data so they do have one, add a new data source that will create a new relationship, or create a parameter-calc field combination