where条件php-mysql中的运算符值

Question

我该怎么做？

SELECT sum(buy-sale) as istock form tbl_product
where istock > 0

我对下面的方法不感兴趣。

SELECT sum(buy-sale) as istock form tbl_product
where sum(buy-sale)> 0

Answer 1

您只需将WHERE替换为HAVING；-(

SELECT SUM(`buy-sale`) AS `istock` FROM tbl_product HAVING `istock` > 0

但这将返回您所有记录的总和。通常情况下，当你根据一个标准进行分组时，你会这样做，比如产品id或其他什么。例如：

-- Find big orders
SELECT 
`order_number`,
SUM(`quantity_ordered`) AS `quantity_sum`,
SUM(`product_price` * `quantity_ordered`) AS `total`
FROM
order_details
GROUP BY 
`order_number`
HAVING 
`total` > 1000;

这可能会有所帮助：https://www.mysqltutorial.org/mysql-having.aspx