If the derivative of a function is zero, is the function a constant function?

See https://math.stackexchange.com/questions/1524724/if-the-derivative-of-a-function-is-zero-is-the-function-a-constant-function#:~:text=If%20the%20domain%20of%20f%20f%20is%20connected%2C,3%29%2C%20but%20not%20constant%20overall.%20%E2%80%93%20Thomas%20Andrews