Linking two tables - a bit different

[Leif]

I understand how I need to link two tables in general. However, I have a bit
different situation.

I have two tables, an Employee table and an EmployeeLocation table (1 to
Many). In the Employee table I have an EmployeeID (primary key) and a
LocationID field. The employee may, over time, change locations. The
EmployeeLocation table has an EmployeeID, LocationID, and StartDate for the
employee at that location. If the employee changes location I want to record
the start date at this new location in the EmployeeLocation table.

If I try to do a join of these two tables on these two fields the fields in
the EmployeeLocation table are read-only. If I create a unique index on the
two fields in the employee table then I'm able to read-write. However, if I
change the employee location then it also changes the location in the
EmployeeLocation table. Instead, I want a new record created since this is a
new location in the EmployeeLocation table, or if the record already exists
then display that record information.

I'm trying to do via a query. So far, either I cannot update the
EmployeeLocation Start date, or the location changes in the EmployeeLocation
table when I change location in the Employee table.

I think I probably could do this via a lot of coding of the StartDate field,
but I was hoping there is a solution just using a query. Has anyone
encountered this type of situation before?

Thanks,
Leif

 

[Steve]

You don't need a LocationID field in the employee table; you are recording
that data in the EmployeeLocation table. The only relationship you need is
to link EmployeeID in TblEmployee to EmployeeID in TblEmployeeLocation.

When an employee changes location all you need do is add a new record to the
EmployeeLocation table.

For data entry you need a form/subform. Base the main form on TblEmployee
and base the subform on TblEmployeeLocation. Set the LinkMaster and
LinkChild fields to EmployeeID. When you go to the form/subform, an employee
will appear in the main form and the subform will display a list of
locations the employee has worked and the start date for each location.

Steve
(e-mail address removed)

 

[Leif]

Steve,

Thanks for your reply.

I think I do need the location ID in the employee table. It is the
employee's current location. For example say the employee ID is 1 and he is
currently at location 1. Also lets say he has been in two other locations in
the past, location 2 and 3. We have (each row below is a record):

Employee table:
ID: 1 Location: 1

EmployeeLocation Table:
ID: 1 Location: 1 Start Date: 1/1/2010
ID: 1 Location: 2 Start Date: 1/1/2009
ID: 1 Location: 3 Start Date: 1/1/2008

I cannot take the latest date from the EmployeeLocation table and assume
that is his current location, since he could switch back to another location
and that would not change his start date.

So adding a recording to the EmployeeLocation table you suggest below is a
programming thing? I was trying to see if I could avoid that, perhaps I
cannot.

I don't want/need a subform for location. It only contains information on
the employee form that will be tried to the employee ID and current location,
therefore it is only a single value, the start date. I don't need to see the
history, I only need to see the start date change if the current employee
location is changed to location where the employee has already been.

Thanks again,
Leif

 

[Steve]

Leif,

From whay you are saying, you have two definitions for Start Date. First you
are saying it is the date an employee moves to a new location; second you
are saying if an employee goes back to a location where he's been before, he
keeps the original start date when he went to that location. In terms of
your database, that won't work! You need to either redefine start date to
one definition or add another field.

Take another look at your example. You have a one-to-many relationship
between employee and employee location. Any time yo have a one-to-many
relationship, data entry is via a subform.

Steve
(e-mail address removed)

 

[david]

I think I do need the location ID in the employee table.

It is the employee's current location.

but I was hoping there is a solution just using a query.

You can't query the employee's CURRENT location
if you want to ADD a new location.

You want a query that returns a blank location,
not the current location.

Try this:
Unique index on location id and start date

Inner join on location table with location table (returns no records)

Left join between employee table and (location table no records)

If it works, that may return an employee record with a blank location, which
you can update to a new current location.

But queries like that are very difficult to use in practice.