Is there a way to reference table rows when a using a combined key.

[FTong]

Newbee here... 

I posted a question a few days ago related to combining more than one column as a key in a table. 

Now it is clear that when two columns are selected as keys they form a completely new key using the values of the two columns selected. 

Follow up Question: 

is there a snipet of code to compare (or ref) a table to just one part of the combined key? 

Description: 

Table 1) Have an old jobs table that exists with about 10 years worth of jobs information (That do not have an ID column in it)  (Ref = Job_No - because they do not repeat)

Table 2) Have a time table that has test times and measurements recorded using the job number as reference  (Many measurements per job for different dates and times).  (Also has about 5 to 6 years worth  of jobs data.)

Table 3) Have a new jobs table that I am trying to use to bring in only the information for the jobs we are currently working on.  (Trying to Reduce amount of data to work with in the app - so it is easier to track as I work on the formulas)

1. This table has a unique ID column assigned to each record.  
2. This table will be used to calculate some rest results for comparison with other tests done at a later time. 
3. Need to bring in the information from table 1 and table 2. 

I am trying to link the information from Table 1 and Table 3 to Table 2.  But do not know how to ref the values to copy the data from tables 1 and table 2 into Table 3. 

Hope this makes sense...