如何正确地将varchar转换为int？

Question

我已经准备好像这样的SQL查询

UPDATE Towar
JOIN TowarZamowienie ON Towar.Tow_id = TowarZamowienie.Tow_id
SET Tow_ilosc = Tow_ilosc - CAST(TowZam_ilosc AS UNSIGNED);

它返回我修改记录：0。我承认我在数据库中有记录

以下是我的表格：

TowarZamowienie 

1   TowZam_id         int(19) AUTO_INCREMENT   
2   Tow_id            int(255)            
3   Zam_id            int(255)             
4   TowZam_ilosc      varchar(10)

---

Towar

1     Tow_id           int(255)
2     Tow_ilosc        int(6)  

这是我的架构http://sqlfiddle.com/#!2/981b4/1

Answer 1

我猜你在ON条款中出错了

试试这个

    ON Towar.Tow_id = TowarZamowienie.TowZam_id

DEMO

Answer 2

试试此代码

  UPDATE Towar
 JOIN 
    TowarZamowienie ON Towar.Tow_id = TowarZamowienie.TowZam_id
 SET 
    Tow_ilosc = Tow_ilosc - CAST(TowZam_ilosc AS UNSIGNED);

Answer 3

为什么不将整数“转换”为Varchar？如果Varchar真的有10个字符而Integer只需要6个数字怎么办？试试这个：

CAST(Tow_ilosc as CHAR(10))

或

CONVERT(Tow_ilosc, CHAR(10))

或只在where子句中使用like

WHERE Tow_ilosc LIKE TowZam_ilosc

（我不喜欢）^^

Answer 4

UPDATE Towar, TowarZamowienie
SET Towar.Tow_ilosc = Towar.Tow_ilosc - CAST(TowarZamowienie.TowZam_ilosc AS UNSIGNED)
WHERE Towar.Tow_id = TowarZamowienie.TowZam_id;

- OR

UPDATE Towar
JOIN TowarZamowienie ON Towar.Tow_id = TowarZamowienie.TowZam_id
SET Tow_ilosc = Tow_ilosc - CAST(TowZam_ilosc AS UNSIGNED);