[英]mySQL two COUNTS in one query with 3 tables involved
我有3张桌子,即:Town; 村; 农民...我需要计算每个村庄有多少个农民,以及每个镇有多少个村庄。 我是php和mysql的新手,所以我的代码仍然很垃圾。.到目前为止,我已经完成了查询代码:
$query = "SELECT *, COUNT(DISTINCT village.villageID) AS cnt_village,
COUNT( farmer.farmerID ) AS cnt_farmers
FROM town LEFT JOIN village ON village.townID = town.townID
LEFT JOIN farmer ON farmer.villageID = village.villageID
GROUP BY town.townID
ORDER BY town.townName";
$result = mysql_query($query);
它已经输出了正确的计数,如下所示:
----TOWN--------VILLAGES----FARMERS-----
| Caibiran | 2 | 23 |
| Culaba | 7 | 39 |
| TOTAL | 9 | 62 |
直到我尝试搜索特定城镇之前,它都能正常工作。 发生的情况是“农民”列的值显示了指定镇的正确值。 但是整个表格仍然显示,其他城镇的农民列显示0。
它显示了这一点:
----TOWN--------VILLAGES----FARMERS-----
| Caibiran | 2 | 23 |
| Culaba | 7 | 0 |
| TOTAL | 9 | 23 |
但是我真正想要的是:
----TOWN--------VILLAGES----FARMERS-----
| Caibiran | 2 | 23 |
| TOTAL | 2 | 23 |
但是我不知道该怎么做。 而且我的想法已经用光了。 请帮我。
这样可以解决问题吗?
SELECT *, COUNT(DISTINCT village.villageID) AS cnt_village,
COUNT( farmer.farmerID ) AS cnt_farmers
FROM town
JOIN village ON village.townID = town.townID
JOIN farmer ON farmer.villageID = village.villageID
GROUP BY town.townID
ORDER BY town.townName
由于将没有任何农民可以加入,因此应将行从结果集中删除。
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