Seeing whether a value exists on another tab

[bmiranda]

I have a list of employee numbers in a column. (These empl numbers contain numbers AND OR letters) I then have 12 more monthly tabs with employee numbers as well. Each employee number has a monthly earnings value next to it. The main tab has about 4500 employees, however, not all of them exist in all months. For example, John Doe may only exist in the DEC month because that's when he was hired. And Jane Doe may only exist in the JAN-JUN tabs because she retired in June.

My problem is this:

In the main tab, I would like to lookup the employee number from a given monthly tab, and IF THE EMPLOYEE EXISTS in a particular monthly tab, input the amount next to the name in the monthly tab, into a box on the main tab. If the name does not exist in a particular monthly tab, I would like to return a "0"

What I've been using was this:

Example for looking up an employee number for the month or March

=LOOKUP(C2,'2011-Mar'!C:C,'2011-Mar'!I:I)

this works well IF AND ONLY IF every employee is the same on all monthly tabs as well as the main tab.

If there is an extra employee on a main tab, and that name doesn't exists for march, in this case, it will return the value of the employee just above it, creating a false entry of data where a 0 should exist.

I hope this explains my problem..I need a drink!