使用 mysql 为每个产品保留的总购买、销售和库存

Question

我正在尝试使用以下 mysql 查询来获取到达产品的总购买、销售和 sotck：

select fk_product_id,
(select sum(quantity) from entry_products where status =0 ) as total_purchase,
(select sum(quantity) from entry_products where status =1)as total_sales,
(select sum(quantity) from entry_products where status =0 ) -
(select sum(quantity) from entry_products where status =1) as stock

from entry_products group by fk_product_id

输出

fk_product_id     total_purchase    total_sales     stock
1                   1700                 660         1040
2                   1700                 660         1040
3                   1700                 660         1040

My Expected Output is
fk_product_id     total_purchase    total_sales     stock
1                   350                  200         150
2                   1100                 460         640
3                   250                  0           250

Answer 1

你需要条件聚合：

select fk_product_id,
       sum(case when status = 0 then quantity else 0 end) as total_purchase,
       sum(case when status = 1 then quantity else 0 end) as total_sales,
       sum(case when status = 0 then quantity else 0 end) - sum(case when status = 1 then quantity else 0 end) as stock
from entry_products 
group by fk_product_id

因为 MySql 将布尔表达式计算为 1 对应 true 或 0 对应 false，所以代码也可以这样写：

select fk_product_id,
       sum((status = 0) * quantity) as total_purchase,
       sum((status = 1) * quantity) as total_sales,
       sum((status = 0) * quantity) - sum((status = 1) * quantity) as stock
from entry_products 
group by fk_product_id