Q:

SUM value group by columns but do not 'aggregate' possible?

I want to sum the number of times thresholds were reached according to 2 different values: date and item. 
Redshift gives me an error asking for more columns in the group by (that I do not want in the group by: "column must appear in the group by clause or be used in an aggregate function"). 
Another issue that would arise is that the code would aggregate my columns and I want to duplicate the SUM number. 
What I have
|------------|--------|------------|
| item_type  | date   |thresh_rchd |
|------------|--------|------------|
|    baby    |monday  |      2     |
|------------|--------|------------|
|    tom     |monday  |      6     |
|------------|--------|------------|
|    baby    |monday  |      8     |
|------------|--------|------------|
|    baby    |tuesday |      4     |
|------------|--------|------------|

What I want:
|------------|--------|------------|-------------|
| item_type  | date   |thresh_rchd |total thresh |
|------------|--------|------------|-------------|
|    baby    |monday  |      2     |     10      |
|------------|--------|------------|-------------|
|    tom     |monday  |      6     |      6      |
|------------|--------|------------|-------------|
|    baby    |monday  |      8     |     10      |
|------------|--------|------------|-------------|
|    baby    |tuesday |      4     |      4      |
|------------|--------|------------|-------------|

A:

you can try like below by using window function
select item_type, date, thresh_rchd, 
       sum(thresh_rchd) over(partition by item_type, date) as total_thresh
from tablename

