[英]Select MAX value from SQL table to apply in another table
我的网站是Prestashop(1.5.6.2)。
根据订购的产品数量,我的某些产品价格可能较低。 我想在某处提到产品的最低价格(所以我需要最大的折扣幅度才能实现这一目标)。
表1(我的价格在此表中)
+------------+-------+
| id.product | price |
+------------+-------+
| 1 | 1000 |
+------------+-------+
表2(我的减少在此表中)
+------------+--------+-----------+
| id.product | amount | reduction |
+------------+--------+-----------+
| 1 | 2 | 100 |
| 1 | 3 | 200 |
| 1 | 4 | 300 |
+------------+--------+-----------+
根据这个例子,我想显示:
产品1从700欧元起
1000 - 300 (which is the maximum reduction on product.id 1) = 700
(我想更新现有价格,因为这是我创建的第二个字段,实际上称为price_from
但我不想使示例过于复杂)
到目前为止,这是我的代码:
UPDATE table1
INNER JOIN table2 ON (table1.id_product = table2.id_product )
SET table1.price = table1.price - (SELECT MAX(table2.reduction) FROM table2 GROUP BY id_product)
有任何想法吗?
如果您只想显示修改后的价格,请使用以下命令:
select t1.id_product, (price - max_reduction) as new_price
from table1 t1 inner join (
select id_product, max(reduction) max_reduction FROM table2
GROUP BY id_product
) t2 on t1.id_product = t2.id_product
如果要修改价格,请尝试以下操作:
update table1 t1, (
select id_product, MAX(t2.reduction) as max_reduction
FROM table2 t2
GROUP BY id_product) t2
SET t1.price = t1.price - t2.max_reduction
WHERE t1.id_product = t2.id_product;
尝试这个:
update table1
inner join (SELECT max(`reduction`) as maxprice, id FROM table2 group by id ) t
on
table1.id = t.id
SET
table1.price = table1.price - t.maxprice
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