有關計數的SQL問題

Question

我想進行查詢，以便僅獲取具有至少50個位置的位置。

我有一張位置表：

Id, City, Country
1, Austin, USA
2, Paris, France

以及通過Location_id連接到Locations的Places表

Id, Name, Details, Location_id
1, The Zoo, blah, 2
2, Big Park, blah, 2

我可以像這樣加入他們：

SELECT place.name，places.id，locations.country，locations.city FROM places INNER JOIN locations on place.location_id = location.id

我如何才能只獲得至少有50個位置的城市的結果並按最大數量排序？

謝謝！

Answer 1

將GROUP BY與HAVING子句一起使用。

SELECT locations.country, locations.city, COUNT(*)
FROM places
     INNER JOIN locations ON places.location_id = locations.id
GROUP BY locations.country, locations.city
HAVING COUNT(*) >= 50

Answer 2

好的，我已經看到上面的答案差不多了，但是有一些錯誤，所以只發布正確的版本即可：

SELECT locations.country, locations.city, COUNT(*) as count_of_places
FROM places
     INNER JOIN locations ON places.location_id = locations.id
GROUP BY locations.country, locations.city
HAVING COUNT(*) >= 50
ORDER BY count_of_places;

Answer 3

您可以使用having子句通過聚合列的值來限制這些行。 另外，MySQL允許您使用懶惰的group by s，因此您可以絕對利用此優勢：

select
    l.country,
    l.city,
    p.name,
    p.details,
    count(*) as number_of_places
from
    locations l
    inner join places p on
        l.id = p.location_id
group by
    l.id
having
    count(*) >= 50
order by
    number_of_places,
    l.country,
    l.city,
    p.name

Answer 4

表現不佳，但應該可以：

FROM (SELECT Locations.id, country,city, count(*) as counter FROM Locations SELECT places.name, places.id, sq.country, sq.city, sq.counter FROM (SELECT Locations.id, country,city, count(*) as counter FROM Locations SELECT places.name, places.id, sq.country, sq.city, sq.counter JOIN Places ON (Locations.Id=Places.Location_id) GROUP BY location.id擁有計數（*）> = 50）AS平方 加入Places ON（sq.id = Places.Location_id） 按櫃台DESC訂購

PS確切的語法可能會有所不同，具體取決於數據庫，我不確定這是否與mysql兼容。