MS Access Age Calculation across tables - database

Question

I'm editing a database template so I can track differences in patient tests across age for the same person.
I retro-fit the "Student Database" template to utilize the forms and macros already created.
I have a patient table that stores all data collected at initial intake : name, date of birth (DOB), etc. and a second table that would track test scores across visits that includes : name, date of visit (DOV) and score information. These are paired so I can pull up information from one patient and see their scores across visits.
What I need to do now is create a query where I can calculate their age when they took the tests.
To do so, I have used expression builder and entered Calculated:([Visit Date]-[DOB])/365
This works for calculating age only if I re-enter the DOB in a new column on the patient visit table
I've tried using DateDiff and using [Patient]![DOB] to recall the data from the other table but I get the same error.
(Calculated age: ([Patient Visit]![Visit Date]-[Patients]![DOB])/365)
Calculated age: (DateDiff("yyyy",[Patients]![DOB],[Patient Visit]![Visit Date]))
Both spit out the error : Enter Parameter Value 'Patients!DOB'
If I enter a date, all data points and patients calculated to have the same DOB that I entered.
How do I let Access know I need it to calculate the date at visit for the DOB of the same patient?
?: Do I need to create a lookup table for the patient ID to match with the DOB and then use that field for calculation?
If there is something wrong with the expression I can fix, that would be ideal. If not, what is the best way to calculate age at visit without having to manually enter in the patient DOB more than once (once in initial uptake and again at each visit).
Thank you in advance.

Answer 1

I found a solution!
I was using 'query' wrong. instead of trying to force it to recognize another table, I needed to add the table to the query upon query creation.
i.e.:
1_ selected 'Query Design'
2_ selected the tables with the required information (entered through forms)
3_ Used `
Patient Name: IIf(IsNull([Last Name]),IIf(IsNull([First Name]),[First Name]),IIf(IsNull([First Name]),[Last Name],[First Name] & " " & [Last Name]))
`
for the first field and
Patient Visit.*
for the second field. By adding "Patient Visit.*" the query will add all fields from the table into the query.
The third field I selected DOB from the Patients table (it was available for selection because I had the two tables selected in the layout initially).
I am now able to use the original
Calculated:([Visit Date]-[DOB])/365
for age calculation w/o any error. I finalized formatting under properties > format > fixed.
Wooo!