Oracle三种rank的区别
rank：1 2 2 2 2 6 rank() over([partition by col1] order by col2) denseRank：1 2 2 2 2 3 dense_rank() over([partition by col1] order by col2) rowNumber：1 2 3 4 5 6 row_number() over([partition by col1] order by col2)
rank：1 2 2 2 2 6 rank() over([partition by col1] order by col2) denseRank：1 2 2 2 2 3 dense_rank() over([partition by col1] order by col2) rowNumber：1 2 3 4 5 6 row_number() over([partition by col1] order by col2)