触发器内insert,delete,update判断执行不同的内容

create trigger tr_a
on a
for insert,update,delere as
begin

IF EXISTS(SELECT 1 FROM inserted) AND NOT EXISTS(SELECT 1 FROM deleted)
BEGIN
  -- 插入触发.
  INSERT INTO B
  SELECT
    inserted.a
  FROM
    inserted;
END;

IF EXISTS(SELECT 1 FROM inserted) AND EXISTS(SELECT 1 FROM deleted)
BEGIN
  -- 更新触发.
  DELETE FROM B WHERE a in ( SELECT a FROM deleted);
  
  INSERT INTO B
  SELECT
    inserted.a
  FROM
    inserted;
END;

IF NOT EXISTS(SELECT 1 FROM inserted) AND EXISTS(SELECT 1 FROM deleted)
BEGIN
  -- 删除触发
  DELETE FROM B WHERE a in ( SELECT a FROM deleted);

END; 

end