Question

所以我试图列出每个客户的数量和名称，这些客户由销售代表65代表，或者当前有订单存在，或者两者都有，并且我一直收到错误。我甚至检查了书中的解决方案，我的代码看起来一样。这个错误告诉我什么？我附上了本书给出的解决方案。 Solution

    mysql> SELECT CUSTOMER_NUM, CUSTOMER_NAME
    -> FROM CUSTOMER
    -> WHERE REP_NUM+'65'
    -> UNION
    -> SELECT C.CUSTOMER_NUM, CUSTOMER_NAME
    -> FROM CUSTOMER C, ORDERS 0
    -> WHERE C.CUSTOMER_NUM=0.CUSTOMER_NUM;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '0
WHERE C.CUSTOMER_NUM=0.CUSTOMER_NUM' at line 6

Answer 1

您有zero作为别名，这是出错的原因。数字不允许别名。我认为您o而不是zero

SELECT CUSTOMER_NUM, CUSTOMER_NAME
     FROM CUSTOMER
     WHERE REP_NUM = '65'  -- also here `=` should be used instead of `+`
     UNION
     SELECT C.CUSTOMER_NUM, CUSTOMER_NAME
     FROM CUSTOMER C, ORDERS o
     WHERE C.CUSTOMER_NUM=o.CUSTOMER_NUM;

Answer 2

使用EXISTS：

select c.*
from customer c
where rep_num = 65 or
      exists (select 1 from orders o where c.customer_num = o.customer_num);

您的具体问题是您使用了数字作为表别名。你应该真的在用一封信。

然而，其他一些事情浮现在脑海中：

union是一种资源匮乏，因为它会导致删除重复项的开销。这个查询不是必需的。
数字，例如65，不应该用单引号括起来 - 这些数字应该用于字符串和日期。
您有一个+，其中要求=。

Answer 3

检查你的语法，它是='65'而不是+ '65'

 mysql> SELECT CUSTOMER_NUM, CUSTOMER_NAME
-> FROM CUSTOMER
-> **WHERE REP_NUM+'65**'
-> UNION
-> SELECT C.CUSTOMER_NUM, CUSTOMER_NAME
-> FROM CUSTOMER C, ORDERS 0
-> WHERE C.CUSTOMER_NUM=0.CUSTOMER_NUM;

我在SQL代码中找不到错误？

3 个答案: