我尝试在mysql上计算两个表之间的值

我尝试使用左联接，但我无法使其成为正确的sql语句，请更正它

我相信您正在寻找左联接

Select sale.preselRef As ref,
  sale.name,
  sale.saledate,
  sale.grandtotal,
  sale.secid,
  sale.invoicetype As typ,
  Sum(sellnote.Paid group by sellnote.Code) As cash,

From sale left joint
  sellnote on ( sale.preselRef = sellnote.Code)

--不要放在现金之后，因为它是select报表中的最后一个。 --分组依据应放在@end

尝试以下操作：

Select sale.preselRef As ref,
    sale.name,
    sale.saledate,
    sale.grandtotal, 
    sale.secid,
    sale.invoicetype As typ,
    Sum(sellnote.Paid) As cash
From sale LEFT JOIN 
    sellnote on ( sale.preselRef = sellnote.Code) 
    GROUP BY sellnote.Code

---

所需的输出是什么？运行此查询可以得到什么？它也不是左关节它的

左关节

。你想实现什么？

Select sale.preselRef As ref,
  sale.name,
  sale.saledate,
  sale.grandtotal,
  sale.secid,
  sale.invoicetype As typ,
  Sum(sellnote.Paid group by sellnote.Code) As cash,

From sale left join
  sellnote on ( sale.preselRef = sellnote.Code)