Two ways of expressing 'only' in Japanese are だけ + positive verb and しか + negative verb. For example, the following sentences both translate to something like 'I drank only tea'.
I recently heard a native speaker use だけしか + negative verb, and Google brings up plenty of hits for this construction. For example:
- お茶だけしか飲まなかった (3)
Is there any difference in meaning between sentences (2) and (3)? Does including 'だけ' just add emphasis?