Make "to" value based on "from" value

[ayla]

I need help creating a query that creates a "to" value.
Have this table:
Manr_f, CC, SD, ED

Manr_f = employee number
CC = Cost Center
SD = "from" date
ED = should be "to" date based on SD

Manr_f,CC, SD, ED
1001,1,6924,7759
1001,2,7760,
1002,1,6924,7589
1002,3,7590,7799
1002,1,7800,
1003,1,6924,

* SD is stored as days from 1/1/1990
* ED column shows the desired result, this column is now empty

Anybody have a solution for me?

 

[Galaxiom]

ED should not be stored because it is a derived value.
Calculate in a query whenever it is required.

ED: DateAdd("d",[ED],#1/1/1990#)