SQL Server：如何更新表b，何时在表a中更新单行？

Question

我创建了一个SQL Server触发器，当他的一个病人改变状态为“杀死”时，应该为医生添加一个杀手。但我不知道如何获得更新的那一行。从现在看来，医生对于他以前曾经患过的每一位患者都会有耐心的++。

我该如何解决这个问题？

SET ANSI_NULLS ON 
GO 
SET QUOTED_IDENTIFIER ON 
GO 

ALTER TRIGGER [dbo].[PatientKilled] 
ON [dbo].[Patient] 
AFTER UPDATE 
AS 
BEGIN 
    DECLARE 

    SET NOCOUNT ON; 

    UPDATE Doctor 
    SET PatientsKilled += 1 
    FROM Doctor d 
    INNER JOIN inserted p ON d.DoctorId = p.DoctorId 
    WHERE p.PatientState = 'Killed' 
END 

Answer 1

字“杀”意味着医生是杀人，但无视这个问题本应该做你所需要的。

您应该检查以前的状态，并且只在计数器改变时才增加计数器。我认为“Killed”是一个永久状态，因此不需要添加逻辑来减少。你应该考虑你是否需要这个。

WITH p AS 
(
SELECT COUNT(*) AS NewKills, 
       I.DoctorId 
FROM INSERTED I JOIN DELETED D 
ON I.PatientId = D.PatientId 
WHERE I.PatientState = 'Killed' 
    AND (D.PatientState <> 'Killed' OR D.PatientState IS NULL) 
GROUP BY I.DoctorId 
) 
UPDATE d 
SET PatientsKilled += NewKills 
FROM Doctor d 
    INNER JOIN p ON d.DoctorId = p.DoctorId 

Answer 2

USE [AD17_Hospital] 
GO 
/****** Object: Trigger [dbo].[PatientKilled] Script Date: 2017-10-21 19:51:32 ******/ 
SET ANSI_NULLS ON 
GO 
SET QUOTED_IDENTIFIER ON 
GO 
ALTER TRIGGER [dbo].[PatientKilled] ON [dbo].[Patient] 
AFTER UPDATE 
AS 
BEGIN 

SET NOCOUNT ON; 
UPDATE Doctor 
SET PatientsKilled (SELECT COUNT(*) FROM Patients WHERE DoctorID = INSERTED.DoctorID AND PatientState = 'Killed') 
FROM Doctor d 

END