Find a non empity value

Dear i have 2 tables :

1) table1: it contains for each month the costcenter of each employee;

fields:

employee-NAME; PERIOD; CDC

XXX MARCH19 Finance

2) table2: it contains for each month the costs of eache employee.

employee-name; period;totalcosts

I have create a key in order to match for each employee name wich costcenter was associated each employee in a period.

The problem is that some periods are missing in table1 so i'd like to find the last period in table 1 to link to table 2. How can i manage it ? any idea ? thanks.

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