I want to use a control in a form such as a combo box or list box to take the values from one field and display them (like the names of clients), but instead of entering a client’s name into another field it enters the corresponding ClientID instead. In short, is there a form of lookup function in base that takes the input from a form’s control and outputs a related field’s value in the same row instead.
There is no control with a function to read one field and write a corresponding field. You can can create a list, for say a listbox, and when selecting an item, for example “red”, it can write out a different value, maybe “01”. But this is all done at design time and not real time.
What you want to do is possible but does require coding your own macros. If not familiar with this, it can be quite a mountain to climb. To see a working sample of this (input is a text box but could easily be a list box), see the answer in this post (click here).