First of all, there is no inherent numbering of rows in MySQL, so selecting "odd" or "even" rows is not possible unless you have a field that numbers them.
If you have such a field, say RowNumber, then use
SELECT * FROM Table WHERE MOD(RowNumber) = 0 for the even rows, or
SELECT * FROM Table WHERE MOD(RowNumber) <> 0 for the odd rows.