What is the difference between clinical depression and schizoid personality disorder?

Depression: Both can show avoidance and withdrawal and isolation with blunted affect, but depression also shows vegetative symptoms such as change in sleep/appetite/energy , and thoughts of despair &self-harm.

Mood: Depression is a mood disorder involving sadness, emptiness, withdrawal, and anhedonia, among other symptoms. Schizoid PD is all about indifference to interpersonal relationships.