Question

这里的逻辑错误是输出显示如下：

+-----------------+-------+----------+-------+
| registration_no | color | producer | count |
+-----------------+-------+----------+-------+
| X23-234         | green | VW       |     2 |
| BC-343          | red   | BMW      |     2 |
| TW-435          | blue  | Ford     |     1 |
| 232-444         | pink  | Army     |     2 |
+-----------------+-------+----------+-------+

正如您所看到的，最小计数是蓝色，我希望它只显示：

| TW-435          | blue  | Ford     |

派生查询不应仅限制关键字嵌套查询。这是我的SQL查询：

mysql> SELECT registration_no, color, producer, COUNT(*) as count 
       FROM car, car_type, booking 
       WHERE car.car_type_id = car_type.car_type_id and booking.car_id = car.car_id 
       GROUP BY car.car_id;

我无法找出解决方案。

Answer 1

按计数（*）排序，然后在第一行限制

SELECT registration_no, color, producer, COUNT(*) as count 
FROM car, car_type, booking 
WHERE car.car_type_id = car_type.car_type_id and booking.car_id =car.car_id 
GROUP BY car.car_id
ORDER BY COUNT(*) ASC
LIMIT 1;

如果你只想要一行，这是有效的。如果你有更多行count(*) = 1，那么你应该使用另一种方法

如果你想显示最高计数只是排序降序

....
ORDER BY COUNT(*) DESC

但在这种情况下，您将获得3行count = 2中的一行，而不是所有三行

Answer 2

按计数排序，只使用limit

的第一个元素

SELECT registration_no, color, producer, COUNT(*) as count 
FROM car
join car_type on car.car_type_id = car_type.car_type_id
JOIN booking on booking.car_id = car.car_id 
GROUP BY car.car_id
order by count asc
limit 1

BTW使用显式连接语法。

Answer 3

我认为您需要这样的查询：

SELECT registration_no, color, producer
FROM (
    SELECT registration_no, color, producer, COUNT(*) as count 
    FROM car, car_type, booking 
    WHERE car.car_type_id = car_type.car_type_id and booking.car_id = car.car_id 
    GROUP BY car.car_id) DT
ORDER BY count
LIMIT 1;

Answer 4

您可以使用此查询来选择最小计数：

select min(count) from (select COUNT(*) as count 
   FROM car, car_type, booking 
   WHERE car.car_type_id = car_type.car_type_id and booking.car_id = car.car_id 
   GROUP BY car.car_id);

Answer 5

mysql> SELECT registration_no, color, producer 
FROM car, car_type, booking 
WHERE car.car_type_id = car_type.car_type_id and booking.car_id =car.car_id 
GROUP BY car.car_id
ORDER BY COUNT(*) ASC
LIMIT 1;
+-----------------+-------+----------+
| registration_no | color | producer |
+-----------------+-------+----------+
| TW-435          | blue  | Ford     |
+-----------------+-------+----------+
1 row in set

MySQL：如何在不使用限制的情况下仅显示最小计数？

5 个答案: