How do you get get absent rows from a SQL table?

I am not sure if I had asked the question correctly in title, but here the proper scenario.

Suppose I have SQL table in which rows are inserted everyday. In these rows there is one column which has one set of values. That means in this column, let's call it Source_system, we receive 20 values each day. Same distinct values everyday. Now is there any way I can get the name of the source system which is not inserted for that day?

EDIT: Sorry for bad English.

via Chebli Mohamed