SQL - 按id计数

Question

我目前正在尝试列出每位兽医参加的访问次数。我必须将兽医的姓名详细信息与参加的访问次数一起包括在内。然后，我必须通过兽医标题对报告进行排序。

访问表格结构：

visit_id, vet_id, pet_id, Visit_Date, Basic_Cost, Symptom, Treatment

兽医表结构：

vet_id, Surname, Forename, Title, Ext_Number, Position, Salary

下面是我创建的初始SQL命令。它不起作用，我想知道如何为上述问题创建一个SQL命令。感谢所有帮助，请注意我使用ms访问。

SELECT vet_id, Title, Forename, Surname, COUNT(vet_id)
FROM visit, vet
ORDER BY Title;

Answer 1

假设你想要所有的兽医，即使他们没有访问过......

SELECT P.vet_id, Title, Forename, Surname, coalesce(COUNT(V.vet_id),0) as VetVisitCount
FROM VET P
LEFT JOIN  Visit V
 on P.Vet_ID = V.Vet_ID
GROUP BY P.vet_id, Title, Forename, Surname
ORDER BY Title;

Answer 2

SELECT vet_id, title, Forename, Surname,
 (SELECT COUNT(visit.vet_id) FROM visit WHERE visit.vet_id = vet.vet_id) AS visits
FROM vet
ORDER BY vet.vet_id;

Answer 3

您需要GROUP BY

SELECT vet_id, Title, Forename, Surname, COUNT(vet_id)
FROM visit, vet
GROUP BY vet_id, Title, Forename, Surname
ORDER BY Title;