I am creating an application with a click to call button on an html page.
There will be one person manning the phone. I want this person to be able to set a variable with a boolian value on my server: 1 is available, 0 is unavailable.
I could create a single field SQL table
but this feels like overkill, or I could read and write to a text file containing just one character.
What is the most correct way to store a single value?
I know it seems like overkill to use a small database table for this.
If your application already uses a database, this is by far the best way to proceed. Your database technology has all kinds of support for storing data so it doesn't get lost. But, don't stand up a database and organize your application to use it just for this one data point; a file will be easier in that case.
(WordPress does something similar; it uses a table called
wp_options containing a lot of one-off settings values.)
I suggest your table contain two columns (or maybe more),
available. Then, if you happen to add another person taking telephone calls, your app will be ready to handle that growth. Your current person can have
agent_id = 0.