DENSE_RANK() without duplication

Question

Here\'s what my data looks like:

| col1 | col2 | denserank | whatiwant |
|------|------|-----------|-----------|
| 1    | 1    | 1         | 1         |
| 2          


        

Answer 1

Try this using window functions:

with t(col1  ,col2) as (
select 1 , 1 union all  
select 2 , 1 union all  
select 3 , 2 union all  
select 4 , 2 union all  
select 5 , 1 union all  
select 6 , 2 union all  
select 7 , 2 union all  
select 8 , 3
)
select t.col1,
    t.col2,
    sum(x) over (
        order by col1
        ) whatyouwant
from (
    select t.*,
        case 
            when col2 = lag(col2) over (
                    order by col1
                    )
                then 0
            else 1
            end x
    from t
    ) t
order by col1;

Produces:

It does a single table read and forms group of consecutive equal col2 values in increasing order of col1 and then finds dense rank on that.

• x: Assign value 0 if previous row's col2 is same as this row's col2 (in order of increasing col1) otherwise 1
• whatyouwant: create groups of equal values of col2 in order of increasing col1 by doing an incremental sum of the value x generated in the last step and that's your output.