MYSQL选择与SUM不同

Question

I am developing a Stocks management application, the Portfolio register table has 4 columns, other than date and registry_key, and it looks like this:

----------------------------------------
| stock_key | user_key | units | price |
----------------------------------------
| fund_a    | user_1   | 1000  | 100.35|
| fund_c    | user_2   | 4000  | 101.55|
| fund_d    | user_3   | 2000  | 105.65|
| fund_a    | user_1   | 1500  | 101.45|
| fund_b    | user_1   | 500   | 103.35|
----------------------------------------

I wish to select the portfolio of user_1 with distinct stock_key. For example:

For user_1 the result should be:

[ 
    {fund_key: "fund_a", units: sum(1000,1500), price: sum(100.35,101.45)},
    {fund_key: "fund_b", units: 500, price: 103.35}
]

Hope the question is understandable. Thanks.

Second Phase

How about I need the price as the aggregate total paid over the number of units. So for user_1 the result would be like:

[ 
    {fund_key: "fund_a", units: sum(1000,1500), price: sum(1000*100.35,1500*101.45)/sum(1000,1500)},
    {fund_key: "fund_b", units: 500, price: 103.35}
]

This is important because once the user has brought more units of the same stock at a lower/higher price than before, the accumulated stocks price is averaged out.

Thanks.

Answer 1

So try:

SELECT stock_key, SUM(units), SUM(units * price) / SUM(units) 
FROM Portfolio 
WHERE user_key = 'user_1' 
GROUP BY stock_key;