Question

所以，我试图创建一个数据库，允许在客户订单或我在供应商处订购时自动添加和减去产品数量。这是我的代码：

select p.productid, p.productname,p.price,
p.quantity + (ifnull(sum(s.quantity),0) - ifnull(sum(o.quantity),0))as 
quantity  
from product p 
left join wholesale.supply s on p.productname = s.productname 
left join wholesale.order o on p.productname = o.productname 
group by p.productname order by quantity

这是没有任何订单的输出：

productid     productname        price     quantity      
   6            Sony X           19700        6
   4       Samsung Galaxy S8     38000        11
   5            LG G6            31500        12

这是我的供应商页面中的输出

   id     productname     quantity
    1        Sony X          10
    2        Sony X          10
    3        Sony X          10
    4        Sony X          10

这是在订单页面

id     productname     quantity
1        Sony X           10
2        Sony X           5

输出现在是：

productid     productname        price     quantity      
   6            Sony X           19700        26
   4       Samsung Galaxy S8     38000        11
   5            LG G6            31500        12

如果你算数学索尼X应该是：

productid     productname        price     quantity      
   6            Sony X           19700        31
   4       Samsung Galaxy S8     38000        11
   5            LG G6            31500        12

我的问题是，数量的值不可靠，就像在示例中一样，我的股票中有Sony X 6pcs。我总共订购了40件。并且客户订购总共15件它应该是31，因为6 + 40 = 46-15 = 31 但它在我的数据库中显示了26个。

Answer 1

如果我们打破您的查询，我们可以看到发生了什么。

drop table if exists p;

create table p (productid int,    productname varchar(20),       price int,    quantity int);
insert into p values     
(   6 ,           'Sony X'         ,  19700 ,       6),
(   4 ,      'Samsung Galaxy S8'   ,  38000 ,      11),
(   5 ,           'LG G6'          ,  31500 ,       12);

drop table if exists s;
create table s (id int,    productname varchar(20),     quantity int);
insert into s values
(    1 ,       'Sony X'  ,        10),
(    2 ,       'Sony X'  ,        10),
(    3 ,       'Sony X'  ,        10),
(    4 ,       'Sony X'  ,        10);

drop table if exists o;
create table o(id  int,   productname varchar(20),     quantity int);
insert into o values
(1 ,       'Sony X'   ,        10),
(2 ,       'Sony X'   ,        5);

MariaDB [sandbox]> select p.productid, p.productname,p.price,
    -> p.quantity
    -> ,ifnull(sum(s.quantity),0) squantity
    -> ,ifnull(sum(o.quantity),0) oquantity
    -> from  p
    -> left join s on p.productname = s.productname
    -> left join o on p.productname = o.productname
    -> group by p.productname
    -> order by quantity
    -> ;
+-----------+-------------------+-------+----------+-----------+-----------+
| productid | productname       | price | quantity | squantity | oquantity |
+-----------+-------------------+-------+----------+-----------+-----------+
|         6 | Sony X            | 19700 |        6 |        80 |        60 |
|         4 | Samsung Galaxy S8 | 38000 |       11 |         0 |         0 |
|         5 | LG G6             | 31500 |       12 |         0 |         0 |
+-----------+-------------------+-------+----------+-----------+-----------+
3 rows in set (0.00 sec)

你可以试试这个

MariaDB [sandbox]> select p.productid,p.productname,p.price,p.quantity, s.*,o.*,p.quantity + ifnull(squantity,0) - ifnull(oquantity,0) qty
    -> from p
    -> left join
    -> (select s.productname sproductname, sum(s.quantity) squantity from s group by s.productname) s on sproductname = p.productname
    -> left join
    -> (select o.productname oproductname, sum(o.quantity) oquantity from o group by o.productname) o on oproductname = p.productname;
+-----------+-------------------+-------+----------+--------------+-----------+--------------+-----------+------+
| productid | productname       | price | quantity | sproductname | squantity | oproductname | oquantity | qty  |
+-----------+-------------------+-------+----------+--------------+-----------+--------------+-----------+------+
|         6 | Sony X            | 19700 |        6 | Sony X       |        40 | Sony X       |        15 |   31 |
|         4 | Samsung Galaxy S8 | 38000 |       11 | NULL         |      NULL | NULL         |      NULL |   11 |
|         5 | LG G6             | 31500 |       12 | NULL         |      NULL | NULL         |      NULL |   12 |
+-----------+-------------------+-------+----------+--------------+-----------+--------------+-----------+------+
3 rows in set (0.00 sec)

Mysql添加和减去不同的列而不重复值

1 个答案: