如何比较两个表的计数

Question

尝试比较两个 table 的计数时遇到问题（使用 SQLite）。

假设我有 table 个像：

对象（NumId是主键）

NumId	Object_category
1	permanent
2	borrowed
3	borrowed
4	borrowed
5	borrowed

借来的（NumObj 是 Foreign Key/Primary Key 引用对象 table）

NumObj	Collection_name
2	collection_alpha
3	collection_betha
4	collection_betha
5	collection_betha

我需要执行的查询是：

"What are the collections with higher number of borrowed objects than quantity of permanent objets?"

我目前的尝试是：

SELECT Collection_name FROM Borrowed
WHERE (SELECT COUNT(Collection_name) FROM Borrowed)> 
(SELECT COUNT(*) FROM Objects WHERE Object_category = 
'permanent')

它从列中返回值，没有按预期工作（本应返回 'collection_betha' 因为拥有 3 个对象，大于现有永久对象的数量 1）。

Answer 1

我会在这里使用条件聚合：

SELECT b.Collection_name
FROM Borrowed b
INNER JOIN Objects o
    ON o.NumId = b.NumObj
GROUP BY b.Collection_name
HAVING SUM(o.Object_category = 'borrowed') > SUM(o.Object_category = 'permanent');

Answer 2

也许加入会有所帮助

SELECT Borrowed.Collection_name
FROM Borrowed 
JOIN Objects 
ON Objects.NumId= Borrowed.NumObj
GROUP BY Borrowed.Collection_name 
HAVING COUNT(NumObj) > 
(SELECT COUNT(*) FROM Objects WHERE Object_category = 'permanent')

如何比较两个表的计数

How to compare count of two tables

sql

database

sqlite