Question

SELECT 
    a.customers_id, b.name, b.office, b.username, a.serial_number, a.id
FROM 
    user_assets AS a
left JOIN 
    customers AS b ON 
        a.customers_id = b.id 
WHERE NOT 
        (b.username LIKE 'Warehouse') 
    AND (serial_number LIKE 'R8%' 
        OR serial_number LIKE 'LR%' 
        OR serial_number LIKE 'R9%')
GROUP BY
    a.customers_id
HAVING (COUNT(a.customers_id) >=2);

查询应查找哪些用户拥有多台计算机。但是，每个用户只显示一条记录，如何显示serial_number列中的所有相关行？

编辑：

已移除and a.customers_id = a.customers_id，因为这是我正在尝试的内容，而$by因此问题无法解决

Answer 1

使用GROUP BY - 顾名思义 - 将结果分组（在您的情况下为user_assets'customer_id）。省略GROUP BY，它应该返回符合您标准的每条记录。

我猜你真正想要的是一种通过各自客户对记录进行分组的方法。您应该使用ORDER BY a.customer_id，然后处理应用程序逻辑中的记录。

编辑一个工作示例是：

SELECT a.id,
       a.customers_id,           
       a.serial_number,
       b.name,
       b.office,
       b.username
  FROM user_assets AS a
  LEFT JOIN customers AS b
    ON a.customers_id = b.id 
 WHERE b.username != 'Warehouse'
   AND ( a.serial_number LIKE 'R8%'
    OR a.serial_number LIKE 'LR%'
    OR a.serial_number LIKE 'R9%' )
 ORDER BY a.customer_id

示例输出：

+----+--------------+---------------+-----+
| id | customers_id | serial_number | ... |
+----+--------------+---------------+-----+
|  3 |           11 | R8-xyz        | ... |
|  4 |           13 | R9-abc        | ... |
|  5 |           13 | R8-xyz        | ... |
|  6 |           13 | LR-abc        | ... |
| .. |           .. | ...           | ... |
| 37 |           21 | LR-abc        | ... |
| 38 |           21 | LR-def        | ... |
+----+--------------+---------------+-----+

Answer 2

您不需要left join和group by，但需要在where子句中使用子查询进行简单的内连接：

select b.customers_id, b.name, b.office, b.username, a.serial_number, a.id
from user_assets a, customers b 
WHERE a.customers_id = b.id 
  and b.username != 'Warehouse' 
  and (serial_number LIKE 'R8%' or serial_number LIKE 'LR%' or serial_number LIKE 'R9%')
  and (select count(1) from user_assets a1 
       where a1.customers_id=b.id
       and (serial_number LIKE 'R8%' or serial_number LIKE 'LR%' or serial_number LIKE 'R9%')  
      ) >= 2

另外，您应该考虑创建和使用目录表asset_types而不是序列号上的like - 谓词。一般来说，它会更有效，也是一种更好的做法。

sql查询左连接记录丢失

2 个答案: