Limit a table's cell's values to two values?

Question

I have a two-column table but I want all values in the first table to be either X or Y, and no other input should be allowed. How can I enforce this?

Answer 1

You can use a validation rule.

Restrict data input by using a validation rule

A Validation Rule on the column as follows will work.

="X" Or ="Y"

Answer 2

You might want to look at

1. Create a validation rule to validate data in a field
2. Validation rules