Question

我有两张桌子股票和促销

库存

JSONObject jsonObject = new JSONObject();
try {
    jsonObject.put("username", "pradyut");
    jsonObject.put("password", "5F4DCC3B5AA765D61D8327DEB882CF99");
} catch (JSONException e) {
    e.printStackTrace();
    Log.i("log", "json exception : " + e.toString());
}


if (jsonObject == null) {
    Log.i("log", "the json object is not null");
    // this part is showing everytime.
} else {
    Log.i("log", "the json object is null");
}

出售

id Name size Qty
1  box1  10  100
2  box2  12  200   
3  box3  14  500
4  box4  16  700

我想在Subtract Qty

之后得到这个结果

库存

id Name size Qty
1  box1  10  1
2  box2  12  2  
3  box3  14  5
4  box4  16  7

帮助！

Answer 1

如果你想存储结果在mysql中你可以（使用关系名称）更新

update Stock as a
inner join Sale as b on a.name = b.name 
set a.Qty = a.Qty -b.Qty

或使用id作为关系

update Stock as a
inner join Sale as b on a.id = b.id 
set a.Qty = a.Qty -b.Qty

或者如果你只想要一个选择，你可以

select a.id, a.name, a.size,  a.Qty -b.Qty as qty
from fromStock as a 
inner join Sale as b on a.id = b.id

在sqlite中，不允许使用内部联接进行更新，因此您可以使用子选择

update Stock 
set Qty = (    select Stock.Qty -Sale.Qty from Stock
                Inner join Sale on  Sale.name = Stock.name )
WHERE
EXISTS (
    SELECT *
    from Stock
                Inner join Sale on  Sale.name = Stock.name 
)

Answer 2

您可以按id和name加入表格，然后简单地减去Qty值。添加了table alias名称以提高可读性

SELECT ST.id, ST.Name, ST.size, (ST.Qty - SA.Qty) AS Qty
FROM Stock ST
INNER JOIN Sale SA ON SA.id = ST.id AND SA.Name = ST.Name

如果您不需要按Name加入，则只能id加入

SELECT ST.id, ST.Name, ST.size, (ST.Qty - SA.Qty) AS Qty
FROM Stock ST
INNER JOIN Sale SA ON SA.id = ST.id

SQLite的

更新

UPDATE Stock 
SET Qty = ( SELECT ST.Qty - SA.Qty
            FROM Stock ST
            INNER JOIN Sale SA ON SA.id = ST.id )
WHERE id IN (SELECT id FROM Stock )

获得this answer

的参考资料

Answer 3

试试这个：

Table A   Table B
ID, ABC   ABC
1, A      A
2, B      A
3, C      C
4, D      E
5, E      F

Answer 4

使用以下查询

Select table.id,table.name,table.size,sum(table.qty) from
(Select id,name,size,qty from stock 
Union
Select id,name,size,qty*-1 from sale) as table group by table.id,table.name,table.size

如何将一个表列值减去其他表列值

4 个答案: