Question

我有一个具有主键-NID的Neighbourhood表和一个具有外键NeighborhoodID的Apartment表。我如何创建一个视图，以显示每个邻域中有多少套公寓。谢谢！

Answer 1

我将加入邻域ID上的表，对其进行分组并计算行数：

CREATE OR REPLACE VIEW neighbourhood_apartments AS
SELECT   n.name, COUNT(*)
FROM     neighbourhood n
JOIN     apartment a ON n.nid = a.neightbourhoodid
GROUP BY n.name

Answer 2

对于neighborhood中的每个id，计算apartment中与neighborhoodid匹配的行：

   SELECT 
     neighborhood.id,
     neighborhood.name, 
     (SELECT COUNT(*) FROM apartment AS a WHERE a.neighborhoodid = n.id) AS counter  
   FROM
     neighborhood AS n

来自两个表的sql视图

2 个答案: