SQL percent of total and weighted average - sql

Question

I have the following postgreSql table stock, there the structure is the following:
| column | pk |
+--------+-----+
| date | yes |
| id | yes |
| type | yes |
| qty | |
| fee | |
The table looks like this:
| date | id | type | qty | cost |
+------------+-----+------+------+------+
| 2015-01-01 | 001 | CB04 | 500 | 2 |
| 2015-01-01 | 002 | CB04 | 1500 | 3 |
| 2015-01-01 | 003 | CB04 | 500 | 1 |
| 2015-01-01 | 004 | CB04 | 100 | 5 |
| 2015-01-01 | 001 | CB02 | 800 | 6 |
| 2015-01-02 | 002 | CB03 | 3100 | 1 |
I want to create a view or query, so that the result looks like this.
The table will show the t_qty, % of total Qty, and weighted fee for each day and each type:
% of total Qty = qty / t_qty
weighted fee = fee * % of total Qty
| date | id | type | qty | cost | t_qty | % of total Qty | weighted fee |
+------------+-----+------+------+------+-------+----------------+--------------+
| 2015-01-01 | 001 | CB04 | 500 | 2 | 2600 | 0.19 | 0.38 |
| 2015-01-01 | 002 | CB04 | 1500 | 3 | 2600 | 0.58 | 1.73 |
| 2015-01-01 | 003 | CB04 | 500 | 1 | 2600 | 0.19 | 0.192 |
| 2015-01-01 | 004 | CB04 | 100 | 5 | 2600 | 0.04 | 0.192 |
| | | | | | | | |
I could do this in Excel, but the dataset is too big to process.

Answer 1

You can use SUM with windows function and some Calculation to make it.
SELECT *,
SUM(qty) OVER (PARTITION BY date ORDER BY date) t_qty,
qty::numeric/SUM(qty) OVER (PARTITION BY date ORDER BY date) ,
fee * (qty::numeric/SUM(qty) OVER (PARTITION BY date ORDER BY date))
FROM T
If you want to Rounding you can use ROUND function.
SELECT *,
SUM(qty) OVER (PARTITION BY date ORDER BY date) t_qty,
ROUND(qty::numeric/SUM(qty) OVER (PARTITION BY date ORDER BY date),3) "% of total Qty",
ROUND(fee * (qty::numeric/SUM(qty) OVER (PARTITION BY date ORDER BY date)),3) "weighted fee"
FROM T
sqlfiddle
[Results]:
| date | id | type | qty | fee | t_qty | % of total Qty | weighted fee |
|------------|-----|------|------|-----|-------|----------------|--------------|
| 2015-01-01 | 001 | CB04 | 500 | 2 | 2600 | 0.192 | 0.385 |
| 2015-01-01 | 002 | CB04 | 1500 | 3 | 2600 | 0.577 | 1.731 |
| 2015-01-01 | 003 | CB04 | 500 | 1 | 2600 | 0.192 | 0.192 |
| 2015-01-01 | 004 | CB04 | 100 | 5 | 2600 | 0.038 | 0.192 |
| 2015-01-02 | 002 | CB03 | 3100 | 1 | 3100 | 1 | 1 |