This sounds a bit like a homework....
Anyhow, there are quite a few differences. To name some from the top of my head:
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- the amount of columns is different
- the order of the same columns returned may be different
- the second one may fail because of wrongly typed column name
- the second one may fail because of mixed case characters column names
- the second one may use (different) index
- the second may return the results without ever accessing the employee table at all
- The amount of data transferred to the client may be different
As said this sounds a bit like homework, so at the moment I'll leave the justifications out from this answer :)