phpMyAdmin shows column value as drop-down when field type is int

I'm editing a table via phpMyAdmin and see that the dID column is allowing me to selec开发者_运维知识库t a value from a drop-down list. I initially set the column as an int.

Why is it doing this?

It is probably a foreign key (constraint), so the choices you have (values that are allowed) are limited to the values in the referenced table.

Just as a guess, perhaps the dropdown list contains values that are found in that column in pre-existing rows of your table. So if there are values that commonly appear, you can select them instead of having to type them in. But that's only a guess.