No Sooner .... Than.
1. Separate. 2. Combined.
1. I reached the station. The train came in.
2. No sooner had I reached the station than the train came in.
1. The bell rang. children ran out.
2. No sooner did the bell ring than the children ran out.
Note. It is a mistake to say: No sooner I reached or No sooner the bell rang. After No sooner an auxiliary verb must be used.