OR语句SQL的优先级

Question

我有以下代码段:

WHERE (Person.WorkGroupId = 2 or Person.RoleId = 2)

我想要发生的是WorkGroupId在Person表上返回第一个出现的2.但是,如果没有a的人为WorkgroupId2,则RoldId在Person表中选择第一个出现2的人.

谢谢

Answer 1

SELECT TOP (1) * FROM 
(
  SELECT TOP (1) *, o = 1
  FROM Person
  WHERE WorkGroupId = 2 

  UNION ALL

  SELECT TOP (1) *, o = 2
  FROM Person 
  AND RoleId = 2
) AS x ORDER BY o;

Answer 2

如果你只使用那个,你会得到多个记录.

我会这样做:(有问题的表只扫描一次)

Select top 1 *
From dbo.SomeTable
where WorkGroupId=2 or RoleId=2
Order by case 
   when WorkGroupId=2 then 1 
   when RoleId=2 then 2 
end