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问题是：当我在脚本 php 中添加此查询时，为什么 mysql 的 cpu 使用率会达到 300% -> 400%？

我想从坐标点（MYLAT，MYLON）中找到某个类别（cat_id）最近的兴趣点（poi_id）

POI（poi）表：

 | poi_id | name | city_id | lat | lon |

相关性表（corr）：

| cat_id | poi_id | city_id |

城市表（城市）

| city_id | name |

脚本：

$lat = MYLAT ; // 我起点的纬度

$lon =麦隆; // 我起点的经度

边界框：

$lon1 = $lon - ($dist/abs(cos(rad2deg($lat)) * 60 * 1.1515));

$lon2 = $lon + ($dist/abs(cos(rad2deg($lat)) * 60 * 1.1515));

$lat1 = $lat - ($dist/ 60 * 1.1515);

$lat2 = $lat + ($dist/ 60 * 1.1515);

当我添加此查询时，CPU 使用率变得疯狂：

SELECT a.poi_id,a.name,a.city_id,g.name,a.lat, a.lon,
((ACOS(SIN($lat * PI() / 180) * SIN(a.lat * PI() / 180) +
COS($lat * PI() / 180) * COS(a.lat * PI() / 180) *
COS(($lon - a.lon) * PI() / 180)) * 180 / PI()) * 69.09) AS distance
FROM poi a JOIN corr c on a.poi_id = c.poi_id JOIN city g on c.city_id = g.city_id 
WHERE  a.lon > $lon1 and a.lon < $lon2
AND a.lat > $lat1 and  a.lat < $lat2
AND c.cat_id = $cat_id
HAVING distance < $dist
ORDER BY distance
LIMIT 20


+----+-------------+-------+--------+----------------------------------+---------+---------+--------------------+------+-----------------------------+
| id | select_type | table | type   | possible_keys                    | key     | key_len | ref                | rows | Extra                       |
+----+-------------+-------+--------+----------------------------------+---------+---------+--------------------+------+-----------------------------+
|  1 | SIMPLE      | a     | range  | poi_id,lat,lon,lat_2             | lat_2   | 14      | NULL               | 6924 | Using where; Using filesort |
|  1 | SIMPLE      | c     | eq_ref | city_id_2,cat_id,poi_id,city_id  | cat_id  | 5       | const,a.poi_id     |    1 |                             |
|  1 | SIMPLE      | g     | eq_ref | PRIMARY                          | PRIMARY | 4       | c.city_id          |    1 | Using where                 |
+----+-------------+-------+--------+----------------------------------+---------+---------+--------------------+------+-----------------------------+



mysql> show profile;
+----------------------+----------+
| Status               | Duration |
+----------------------+----------+
| starting             | 0.000138 |
| checking permissions | 0.000010 |
| checking permissions | 0.000006 |
| checking permissions | 0.000008 |
| Opening tables       | 0.000028 |
| System lock          | 0.000015 |
| init                 | 0.000043 |
| optimizing           | 0.000023 |
| statistics           | 0.000221 |
| preparing            | 0.000024 |
| Creating tmp table   | 0.000029 |
| executing            | 0.000005 |
| Copying to tmp table | 0.174197 |
| Sorting result       | 0.000066 |
| Sending data         | 0.000065 |
| end                  | 0.000006 |
| removing tmp table   | 0.000010 |
| end                  | 0.000006 |
| query end            | 0.000005 |
| closing tables       | 0.000011 |
| freeing items        | 0.000077 |
| logging slow query   | 0.000005 |
| cleaning up          | 0.000006 |
+----------------------+----------+
23 rows in set (0.00 sec)
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